Test if string is a number in Ruby on Rails

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91

I have the following in my application controller:

def is_number?(object)

  true if Float(object) rescue false

end

and the following condition in my controller:

if mystring.is_number?



end

The condition is throwing an undefined method error. I'm guessing I've defined is_number in the wrong place...?

ruby-on-rails ruby string integer

share|improve this question

edited Jun 3 '14 at 2:58

user664833

11k1771114

asked Apr 14 '11 at 9:56

Jamie BuchananJamie Buchanan

2,24821622

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  I know a lot of people are here because of codeschool's Rails for Zombies Testing class. Just wait for him to keep explaining. The tests aren't supposed to pass --- its OK to have you test fail in error, you can always patch rails to invent methods such as self.is_number?
  
  – boulder_ruby
  Feb 28 '13 at 19:33
  

  
  
  
  


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  The accepted answer fails on cases like "1,000" and is a 39x slower than using a regex approach. See my answer below.
  
  – pthamm
  Feb 19 '16 at 23:10
  

  
  
  
  

add a comment | 

91

I have the following in my application controller:

def is_number?(object)

  true if Float(object) rescue false

end

and the following condition in my controller:

if mystring.is_number?



end

The condition is throwing an undefined method error. I'm guessing I've defined is_number in the wrong place...?

ruby-on-rails ruby string integer

share|improve this question

edited Jun 3 '14 at 2:58

user664833

11k1771114

asked Apr 14 '11 at 9:56

Jamie BuchananJamie Buchanan

2,24821622

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  I know a lot of people are here because of codeschool's Rails for Zombies Testing class. Just wait for him to keep explaining. The tests aren't supposed to pass --- its OK to have you test fail in error, you can always patch rails to invent methods such as self.is_number?
  
  – boulder_ruby
  Feb 28 '13 at 19:33
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The accepted answer fails on cases like "1,000" and is a 39x slower than using a regex approach. See my answer below.
  
  – pthamm
  Feb 19 '16 at 23:10
  

  
  
  
  

add a comment | 

91

91

91

22

I have the following in my application controller:

def is_number?(object)

  true if Float(object) rescue false

end

and the following condition in my controller:

if mystring.is_number?



end

The condition is throwing an undefined method error. I'm guessing I've defined is_number in the wrong place...?

ruby-on-rails ruby string integer

share|improve this question

edited Jun 3 '14 at 2:58

user664833

11k1771114

asked Apr 14 '11 at 9:56

Jamie BuchananJamie Buchanan

2,24821622

I have the following in my application controller:

def is_number?(object)

  true if Float(object) rescue false

end

and the following condition in my controller:

if mystring.is_number?



end

The condition is throwing an undefined method error. I'm guessing I've defined is_number in the wrong place...?

ruby-on-rails ruby string integer

ruby-on-rails ruby string integer

share|improve this question

edited Jun 3 '14 at 2:58

user664833

11k1771114

asked Apr 14 '11 at 9:56

Jamie BuchananJamie Buchanan

2,24821622

share|improve this question

edited Jun 3 '14 at 2:58

user664833

11k1771114

asked Apr 14 '11 at 9:56

Jamie BuchananJamie Buchanan

2,24821622

share|improve this question

share|improve this question

edited Jun 3 '14 at 2:58

user664833

11k1771114

edited Jun 3 '14 at 2:58

user664833

11k1771114

edited Jun 3 '14 at 2:58

user664833

11k1771114

11k1771114

asked Apr 14 '11 at 9:56

Jamie BuchananJamie Buchanan

2,24821622

asked Apr 14 '11 at 9:56

Jamie BuchananJamie Buchanan

2,24821622

asked Apr 14 '11 at 9:56

Jamie BuchananJamie Buchanan

2,24821622

2,24821622

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  I know a lot of people are here because of codeschool's Rails for Zombies Testing class. Just wait for him to keep explaining. The tests aren't supposed to pass --- its OK to have you test fail in error, you can always patch rails to invent methods such as self.is_number?
  
  – boulder_ruby
  Feb 28 '13 at 19:33
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The accepted answer fails on cases like "1,000" and is a 39x slower than using a regex approach. See my answer below.
  
  – pthamm
  Feb 19 '16 at 23:10
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  I know a lot of people are here because of codeschool's Rails for Zombies Testing class. Just wait for him to keep explaining. The tests aren't supposed to pass --- its OK to have you test fail in error, you can always patch rails to invent methods such as self.is_number?
  
  – boulder_ruby
  Feb 28 '13 at 19:33
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The accepted answer fails on cases like "1,000" and is a 39x slower than using a regex approach. See my answer below.
  
  – pthamm
  Feb 19 '16 at 23:10
  

  
  
  
  

4

4

I know a lot of people are here because of codeschool's Rails for Zombies Testing class. Just wait for him to keep explaining. The tests aren't supposed to pass --- its OK to have you test fail in error, you can always patch rails to invent methods such as self.is_number?

– boulder_ruby
Feb 28 '13 at 19:33

I know a lot of people are here because of codeschool's Rails for Zombies Testing class. Just wait for him to keep explaining. The tests aren't supposed to pass --- its OK to have you test fail in error, you can always patch rails to invent methods such as self.is_number?

– boulder_ruby
Feb 28 '13 at 19:33

The accepted answer fails on cases like "1,000" and is a 39x slower than using a regex approach. See my answer below.

– pthamm
Feb 19 '16 at 23:10

The accepted answer fails on cases like "1,000" and is a 39x slower than using a regex approach. See my answer below.

– pthamm
Feb 19 '16 at 23:10

add a comment | 

12 Answers
12

active

oldest

votes

175

Create is_number? Method.

Create a helper method:

def is_number? string

  true if Float(string) rescue false

end

And then call it like this:

my_string = '12.34'



is_number?( my_string )

# => true

Extend String Class.

If you want to be able to call is_number? directly on the string instead of passing it as a param to your helper function, then you need to define is_number? as an extension of the String class, like so:

class String

  def is_number?

    true if Float(self) rescue false

  end

end

And then you can call it with:

my_string.is_number?

# => true

share|improve this answer

edited Jul 3 '15 at 11:44

Joshua Pinter

25.5k9145174

answered Apr 14 '11 at 10:13

Jakob SJakob S

16.1k23535

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  This is a bad idea. "330.346.11".to_f # => 330.346
  
  – epochwolf
  Nov 2 '11 at 23:15
  

  
  
  
  


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  There is no to_f in the above, and Float() doesn't exhibit that behavior: Float("330.346.11") raises ArgumentError: invalid value for Float(): "330.346.11"
  
  – Jakob S
  Nov 3 '11 at 10:29
  
  
  

  
  
  
  


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  If you use that patch, I'd rename it to numeric?, to stay in line with ruby naming conventions (Numeric classes inherit from Numeric, is_ prefixes are javaish).
  
  – Konrad Reiche
  Jun 24 '12 at 18:34
  

  
  
  
  


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  Not really relevant to the original question, but I'd probably put the code in lib/core_ext/string.rb.
  
  – Jakob S
  Aug 7 '12 at 8:48
  

  
  
  
  


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  I don't think the is_number?(string) bit works Ruby 1.9. Maybe that is part of Rails or 1.8? String.is_a?(Numeric) works. See also stackoverflow.com/questions/2095493/….
  
  – Ross Attrill
  Jun 16 '14 at 7:10
  
  
  

  
  
  
  

 | 
show 7 more comments

29

class String

  def numeric?

    return true if self =~ /Ad+Z/

    true if Float(self) rescue false

  end

end  



p "1".numeric?  # => true

p "1.2".numeric? # => true

p "5.4e-29".numeric? # => true

p "12e20".numeric? # true

p "1a".numeric? # => false

p "1.2.3.4".numeric? # => false

share|improve this answer

edited May 1 '15 at 20:40

Marius Butuc

10.2k1868107

answered Jul 25 '12 at 16:02

hipertrackerhipertracker

2,1182212

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  /^d+$/ is not a safe regexp in Ruby, /Ad+Z/ is. (e.g. "42nsome text" would return true)
  
  – Timothee A
  Sep 1 '14 at 15:18
  

  
  
  
  


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  To clarify on @TimotheeA's comment, it is safe to use /^d+$/ if dealing with lines but in this case it's about beginning and end of a string, thus /Ad+Z/.
  
  – Julio
  Oct 9 '14 at 20:09
  
  
  

  
  
  
  


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  Shouldn't answers be edited to change the actual answer BY the responder? changing the answer in an edit if you're not the responder seems...possibly underhanded and should be out of bounds.
  
  – jaydel
  Jul 20 '16 at 15:43
  

  
  
  
  


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  Where should I put these codes?
  
  – zx1986
  Jul 7 '17 at 4:10
  

  
  
  
  


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  Z allows to have n at the end of the string, so "123n" will pass validation, regardless that it's not fully numeric. But if you use z then it will be more correct regexp: /Ad+z/
  
  – SunnyMagadan
  Aug 14 '17 at 9:14
  

  
  
  
  

add a comment | 

26

Here's a benchmark for common ways to address this problem. Note which one you should use probably depends on the ratio of false cases expected.

1. If they are relatively uncommon casting is definitely fastest.


2. If false cases are common and you are just checking for ints, comparison vs a transformed state is a good option.


3. If false cases are common and you are checking floats, regexp is probably the way to go

If performance doesn't matter use what you like. :-)

Integer checking details:

# 1.9.3-p448

#

# Calculating -------------------------------------

#                 cast     57485 i/100ms

#            cast fail      5549 i/100ms

#                 to_s     47509 i/100ms

#            to_s fail     50573 i/100ms

#               regexp     45187 i/100ms

#          regexp fail     42566 i/100ms

# -------------------------------------------------

#                 cast  2353703.4 (±4.9%) i/s -   11726940 in   4.998270s

#            cast fail    65590.2 (±4.6%) i/s -     327391 in   5.003511s

#                 to_s  1420892.0 (±6.8%) i/s -    7078841 in   5.011462s

#            to_s fail  1717948.8 (±6.0%) i/s -    8546837 in   4.998672s

#               regexp  1525729.9 (±7.0%) i/s -    7591416 in   5.007105s

#          regexp fail  1154461.1 (±5.5%) i/s -    5788976 in   5.035311s



require 'benchmark/ips'



int = '220000'

bad_int = '22.to.2'



Benchmark.ips do |x|

  x.report('cast') do

    Integer(int) rescue false

  end



  x.report('cast fail') do

    Integer(bad_int) rescue false

  end



  x.report('to_s') do

    int.to_i.to_s == int

  end



  x.report('to_s fail') do

    bad_int.to_i.to_s == bad_int

  end



  x.report('regexp') do

    int =~ /^d+$/

  end



  x.report('regexp fail') do

    bad_int =~ /^d+$/

  end

end

Float checking details:

# 1.9.3-p448

#

# Calculating -------------------------------------

#                 cast     47430 i/100ms

#            cast fail      5023 i/100ms

#                 to_s     27435 i/100ms

#            to_s fail     29609 i/100ms

#               regexp     37620 i/100ms

#          regexp fail     32557 i/100ms

# -------------------------------------------------

#                 cast  2283762.5 (±6.8%) i/s -   11383200 in   5.012934s

#            cast fail    63108.8 (±6.7%) i/s -     316449 in   5.038518s

#                 to_s   593069.3 (±8.8%) i/s -    2962980 in   5.042459s

#            to_s fail   857217.1 (±10.0%) i/s -    4263696 in   5.033024s

#               regexp  1383194.8 (±6.7%) i/s -    6884460 in   5.008275s

#          regexp fail   723390.2 (±5.8%) i/s -    3613827 in   5.016494s



require 'benchmark/ips'



float = '12.2312'

bad_float = '22.to.2'



Benchmark.ips do |x|

  x.report('cast') do

    Float(float) rescue false

  end



  x.report('cast fail') do

    Float(bad_float) rescue false

  end



  x.report('to_s') do

    float.to_f.to_s == float

  end



  x.report('to_s fail') do

    bad_float.to_f.to_s == bad_float

  end



  x.report('regexp') do

    float =~ /^[-+]?[0-9]*.?[0-9]+$/

  end



  x.report('regexp fail') do

    bad_float =~ /^[-+]?[0-9]*.?[0-9]+$/

  end

end

share|improve this answer

answered Nov 8 '13 at 1:22

Matt SandersMatt Sanders

4,0772133

add a comment | 

14

Relying on the raised exception is not the fastest, readable nor reliable solution.

I'd do the following :

my_string.should =~ /^[0-9]+$/

share|improve this answer

answered Apr 14 '11 at 10:20

Damien MATHIEUDamien MATHIEU

24k126586

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  This only works for positive integers, however. Values like '-1', '0.0', or '1_000' all return false even though they are valid numeric values. You're looking at something like /^[-.0-9]+$/, but that erroneously accepts '--'.
  
  – Jakob S
  Apr 14 '11 at 11:03
  

  
  
  
  


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  From Rails 'validates_numericality_of': raw_value.to_s =~ /A[+-]?d+Z/
  
  – Morten
  Aug 17 '12 at 20:09
  

  
  
  
  


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  NoMethodError: undefined method `should' for "asd":String
  
  – sergserg
  Oct 9 '14 at 22:08
  

  
  
  
  


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  In the latest rspec, this becomes expect(my_string).to match(/^[0-9]+$/)
  
  – Damien MATHIEU
  Oct 10 '14 at 8:55
  

  
  
  
  


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  I like: my_string =~ /A-?(d+)?.?d+Z/ it lets you do '.1', '-0.1', or '12' but not '' or '-' or '.'
  
  – Josh
  Sep 2 '16 at 0:05
  

  
  
  
  

 | 
show 1 more comment

6

no you're just using it wrong. your is_number? has an argument. you called it without the argument

you should be doing is_number?(mystring)

share|improve this answer

edited Apr 14 '11 at 10:22

answered Apr 14 '11 at 9:58

corrodedcorroded

15k1772128

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  Based on the is_number? method in the question, using is_a? is not giving the correct answer. If mystring is indeed a String, mystring.is_a?(Integer) will always be false. It looks like he wants a result like is_number?("12.4") #=> true
  
  – Jakob S
  Apr 14 '11 at 10:15
  
  
  

  
  
  
  


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  mmm good point, lemme update that
  
  – corroded
  Apr 14 '11 at 10:20
  

  
  
  
  


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  Jakob S is correct. mystring is indeed always a string, but may be comprise of just numbers. perhaps my question should have been is_numeric? so as not to confuse the datatype
  
  – Jamie Buchanan
  Apr 14 '11 at 10:23
  

  
  
  
  

add a comment | 

5

Tl;dr: Use a regex approach. It is 39x faster than the rescue approach in the accepted answer and also handles cases like "1,000"

def regex_is_number? string

  no_commas =  string.gsub(',', '')

  matches = no_commas.match(/-?d+(?:.d+)?/)

  if !matches.nil? && matches.size == 1 && matches[0] == no_commas

    true

  else

    false

  end

end

--

The accepted answer by @Jakob S works for the most part, but catching exceptions can be really slow. In addition, the rescue approach fails on a string like "1,000".

Let's define the methods:

def rescue_is_number? string

  true if Float(string) rescue false

end



def regex_is_number? string

  no_commas =  string.gsub(',', '')

  matches = no_commas.match(/-?d+(?:.d+)?/)

  if !matches.nil? && matches.size == 1 && matches[0] == no_commas

    true

  else

    false

  end

end

And now some test cases:

test_cases = {

  true => ["5.5", "23", "-123", "1,234,123"],

  false => ["hello", "99designs", "(123)456-7890"]

}

And a little code to run the test cases:

test_cases.each do |expected_answer, cases|

  cases.each do |test_case|

    if rescue_is_number?(test_case) != expected_answer

      puts "**rescue_is_number? got #{test_case} wrong**"

    else

      puts "rescue_is_number? got #{test_case} right"

    end



    if regex_is_number?(test_case) != expected_answer

      puts "**regex_is_number? got #{test_case} wrong**"

    else

      puts "regex_is_number? got #{test_case} right"

    end  

  end

end

Here is the output of the test cases:

rescue_is_number? got 5.5 right

regex_is_number? got 5.5 right

rescue_is_number? got 23 right

regex_is_number? got 23 right

rescue_is_number? got -123 right

regex_is_number? got -123 right

**rescue_is_number? got 1,234,123 wrong**

regex_is_number? got 1,234,123 right

rescue_is_number? got hello right

regex_is_number? got hello right

rescue_is_number? got 99designs right

regex_is_number? got 99designs right

rescue_is_number? got (123)456-7890 right

regex_is_number? got (123)456-7890 right

Time to do some performance benchmarks:

Benchmark.ips do |x|



  x.report("rescue") { test_cases.values.flatten.each { |c| rescue_is_number? c } }

  x.report("regex") { test_cases.values.flatten.each { |c| regex_is_number? c } }



  x.compare!

end

And the results:

Calculating -------------------------------------

              rescue   128.000  i/100ms

               regex     4.649k i/100ms

-------------------------------------------------

              rescue      1.348k (±16.8%) i/s -      6.656k

               regex     52.113k (± 7.8%) i/s -    260.344k



Comparison:

               regex:    52113.3 i/s

              rescue:     1347.5 i/s - 38.67x slower

share|improve this answer

answered Feb 19 '16 at 23:07

pthammpthamm

1,5421814

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  Thanks for the benchmark. The accepted answer has the advantage of accepting inputs like 5.4e-29. I guess your regex could be tweaked to accept those also.
  
  – Jodi
  Feb 24 '16 at 16:27
  

  
  
  
  


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  Handling cases like 1,000 is really hard, since it depends on user intention. There are many, many ways for humans to format numbers. Is 1,000 about equal to 1000, or about equal to 1? Most of the world says it's about 1, not a way to show the integer 1000.
  
  – James Moore
  Feb 25 '17 at 18:59
  

  
  
  
  

add a comment | 

4

this is how i do it, but i think too there must be a better way

object.to_i.to_s == object || object.to_f.to_s == object

share|improve this answer

answered Apr 14 '11 at 9:58

antpawantpaw

10k84278

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  It does not recognize floating notation, e.g. 1.2e+35.
  
  – hipertracker
  Jul 25 '12 at 16:13
  

  
  
  
  

add a comment | 

4

In rails 4, you need to put
require File.expand_path('../../lib', __FILE__) + '/ext/string'
in your config/application.rb

share|improve this answer

answered May 19 '14 at 4:57

jcyejcye

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  actually you don't need to do this, you could just put string.rb in "initializers" and it works!
  
  – mahatmanich
  Jun 16 '14 at 8:32
  

  
  
  
  


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  That's it! so cool!
  
  – zx1986
  Jul 7 '17 at 6:14
  

  
  
  
  

add a comment | 

3

If you prefer not to use exceptions as part of the logic, you might try this:

class String

   def numeric?

    !!(self =~ /^-?d+(.d*)?$/)

  end

end

Or, if you want it to work across all object classes, replace class String with class Object an convert self to a string: !!(self.to_s =~ /^-?d+(.d*)?$/)

share|improve this answer

edited Apr 13 '17 at 2:50

answered Jun 7 '13 at 4:20

Mark SchneiderMark Schneider

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  Whats the purpose of negate and do nil? zero is trurthy on ruby, so you can do just !!(self =~ /^-?d+(.d*)?$/)
  
  – Arnold Roa
  Apr 11 '17 at 14:37
  

  
  
  
  


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  Using !! certainly works. At least one Ruby style guide (github.com/bbatsov/ruby-style-guide) suggested avoiding !! in favor of .nil? for readability, but I've seen !! used in popular repositories, and I think it is a fine way to convert to boolean. I've edited the answer.
  
  – Mark Schneider
  Apr 13 '17 at 2:52
  

  
  
  
  

add a comment | 

0

As of Ruby 2.6.0, the numeric cast-methods have an optional exception-argument [1]. This enables us to use the built-in methods without using exceptions as control flow:

Float('x') # => ArgumentError (invalid value for Float(): "x")

Float('x', exception: false) # => nil

Therefore, you don't have to define your own method, but can directly check variables like e.g.

if Float(my_var, exception: false)

  # do something if my_var is a float

end

share|improve this answer

answered Jan 3 at 12:59

TimitryTimitry

431614

add a comment | 

-2

use the following function:

def is_numeric? val

    return val.try(:to_f).try(:to_s) == val

end

so,

is_numeric? "1.2f" = false

is_numeric? "1.2" = true

is_numeric? "12f" = false

is_numeric? "12" = true

share|improve this answer

answered Dec 22 '14 at 12:19

Rajesh PaulRajesh Paul

3,88562743

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This will fail if val is "0". Also note that the method .try isn't part of the Ruby core library and is only available if you're including ActiveSupport.
  
  – GMA
  Sep 17 '15 at 12:51
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In fact, it also fails for "12", so your fourth example in this question is wrong. "12.10" and "12.00" fail too.
  
  – GMA
  Sep 17 '15 at 12:52
  

  
  
  
  

add a comment | 

-5

How dumb is this solution?

def is_number?(i)

  begin

    i+0 == i

  rescue TypeError

    false

  end

end

share|improve this answer

answered Oct 6 '13 at 12:16

donvnielsendonvnielsen

837

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  This is sub-optimal because using '.respond_to?(:+)' is always better then failing and catching an exception on a specific method (:+) call. This might also fail for a variety of reasons were the Regex and conversion methods don't.
  
  – Sqeaky
  Apr 28 '14 at 17:17
  

  
  
  
  

add a comment | 

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175

Create is_number? Method.

Create a helper method:

def is_number? string

  true if Float(string) rescue false

end

And then call it like this:

my_string = '12.34'



is_number?( my_string )

# => true

Extend String Class.

If you want to be able to call is_number? directly on the string instead of passing it as a param to your helper function, then you need to define is_number? as an extension of the String class, like so:

class String

  def is_number?

    true if Float(self) rescue false

  end

end

And then you can call it with:

my_string.is_number?

# => true

share|improve this answer

edited Jul 3 '15 at 11:44

Joshua Pinter

25.5k9145174

answered Apr 14 '11 at 10:13

Jakob SJakob S

16.1k23535

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  This is a bad idea. "330.346.11".to_f # => 330.346
  
  – epochwolf
  Nov 2 '11 at 23:15
  

  
  
  
  


• 
  
  
  

  
  11
  

  
  
  
  
  
  

  
  
  There is no to_f in the above, and Float() doesn't exhibit that behavior: Float("330.346.11") raises ArgumentError: invalid value for Float(): "330.346.11"
  
  – Jakob S
  Nov 3 '11 at 10:29
  
  
  

  
  
  
  


• 
  
  
  

  
  6
  

  
  
  
  
  
  

  
  
  If you use that patch, I'd rename it to numeric?, to stay in line with ruby naming conventions (Numeric classes inherit from Numeric, is_ prefixes are javaish).
  
  – Konrad Reiche
  Jun 24 '12 at 18:34
  

  
  
  
  


• 
  
  
  

  
  9
  

  
  
  
  
  
  

  
  
  Not really relevant to the original question, but I'd probably put the code in lib/core_ext/string.rb.
  
  – Jakob S
  Aug 7 '12 at 8:48
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I don't think the is_number?(string) bit works Ruby 1.9. Maybe that is part of Rails or 1.8? String.is_a?(Numeric) works. See also stackoverflow.com/questions/2095493/….
  
  – Ross Attrill
  Jun 16 '14 at 7:10
  
  
  

  
  
  
  

 | 
show 7 more comments

175

Create is_number? Method.

Create a helper method:

def is_number? string

  true if Float(string) rescue false

end

And then call it like this:

my_string = '12.34'



is_number?( my_string )

# => true

Extend String Class.

If you want to be able to call is_number? directly on the string instead of passing it as a param to your helper function, then you need to define is_number? as an extension of the String class, like so:

class String

  def is_number?

    true if Float(self) rescue false

  end

end

And then you can call it with:

my_string.is_number?

# => true

share|improve this answer

edited Jul 3 '15 at 11:44

Joshua Pinter

25.5k9145174

answered Apr 14 '11 at 10:13

Jakob SJakob S

16.1k23535

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  This is a bad idea. "330.346.11".to_f # => 330.346
  
  – epochwolf
  Nov 2 '11 at 23:15
  

  
  
  
  


• 
  
  
  

  
  11
  

  
  
  
  
  
  

  
  
  There is no to_f in the above, and Float() doesn't exhibit that behavior: Float("330.346.11") raises ArgumentError: invalid value for Float(): "330.346.11"
  
  – Jakob S
  Nov 3 '11 at 10:29
  
  
  

  
  
  
  


• 
  
  
  

  
  6
  

  
  
  
  
  
  

  
  
  If you use that patch, I'd rename it to numeric?, to stay in line with ruby naming conventions (Numeric classes inherit from Numeric, is_ prefixes are javaish).
  
  – Konrad Reiche
  Jun 24 '12 at 18:34
  

  
  
  
  


• 
  
  
  

  
  9
  

  
  
  
  
  
  

  
  
  Not really relevant to the original question, but I'd probably put the code in lib/core_ext/string.rb.
  
  – Jakob S
  Aug 7 '12 at 8:48
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I don't think the is_number?(string) bit works Ruby 1.9. Maybe that is part of Rails or 1.8? String.is_a?(Numeric) works. See also stackoverflow.com/questions/2095493/….
  
  – Ross Attrill
  Jun 16 '14 at 7:10
  
  
  

  
  
  
  

 | 
show 7 more comments

175

175

175

Create is_number? Method.

Create a helper method:

def is_number? string

  true if Float(string) rescue false

end

And then call it like this:

my_string = '12.34'



is_number?( my_string )

# => true

Extend String Class.

If you want to be able to call is_number? directly on the string instead of passing it as a param to your helper function, then you need to define is_number? as an extension of the String class, like so:

class String

  def is_number?

    true if Float(self) rescue false

  end

end

And then you can call it with:

my_string.is_number?

# => true

share|improve this answer

edited Jul 3 '15 at 11:44

Joshua Pinter

25.5k9145174

answered Apr 14 '11 at 10:13

Jakob SJakob S

16.1k23535

Create is_number? Method.

Create a helper method:

def is_number? string

  true if Float(string) rescue false

end

And then call it like this:

my_string = '12.34'



is_number?( my_string )

# => true

Extend String Class.

If you want to be able to call is_number? directly on the string instead of passing it as a param to your helper function, then you need to define is_number? as an extension of the String class, like so:

class String

  def is_number?

    true if Float(self) rescue false

  end

end

And then you can call it with:

my_string.is_number?

# => true

share|improve this answer

edited Jul 3 '15 at 11:44

Joshua Pinter

25.5k9145174

answered Apr 14 '11 at 10:13

Jakob SJakob S

16.1k23535

share|improve this answer

share|improve this answer

edited Jul 3 '15 at 11:44

Joshua Pinter

25.5k9145174

edited Jul 3 '15 at 11:44

Joshua Pinter

25.5k9145174

edited Jul 3 '15 at 11:44

Joshua Pinter

25.5k9145174

25.5k9145174

answered Apr 14 '11 at 10:13

Jakob SJakob S

16.1k23535

answered Apr 14 '11 at 10:13

Jakob SJakob S

16.1k23535

answered Apr 14 '11 at 10:13

Jakob SJakob S

16.1k23535

16.1k23535

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  This is a bad idea. "330.346.11".to_f # => 330.346
  
  – epochwolf
  Nov 2 '11 at 23:15
  

  
  
  
  


• 
  
  
  

  
  11
  

  
  
  
  
  
  

  
  
  There is no to_f in the above, and Float() doesn't exhibit that behavior: Float("330.346.11") raises ArgumentError: invalid value for Float(): "330.346.11"
  
  – Jakob S
  Nov 3 '11 at 10:29
  
  
  

  
  
  
  


• 
  
  
  

  
  6
  

  
  
  
  
  
  

  
  
  If you use that patch, I'd rename it to numeric?, to stay in line with ruby naming conventions (Numeric classes inherit from Numeric, is_ prefixes are javaish).
  
  – Konrad Reiche
  Jun 24 '12 at 18:34
  

  
  
  
  


• 
  
  
  

  
  9
  

  
  
  
  
  
  

  
  
  Not really relevant to the original question, but I'd probably put the code in lib/core_ext/string.rb.
  
  – Jakob S
  Aug 7 '12 at 8:48
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I don't think the is_number?(string) bit works Ruby 1.9. Maybe that is part of Rails or 1.8? String.is_a?(Numeric) works. See also stackoverflow.com/questions/2095493/….
  
  – Ross Attrill
  Jun 16 '14 at 7:10
  
  
  

  
  
  
  

 | 
show 7 more comments

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  This is a bad idea. "330.346.11".to_f # => 330.346
  
  – epochwolf
  Nov 2 '11 at 23:15
  

  
  
  
  


• 
  
  
  

  
  11
  

  
  
  
  
  
  

  
  
  There is no to_f in the above, and Float() doesn't exhibit that behavior: Float("330.346.11") raises ArgumentError: invalid value for Float(): "330.346.11"
  
  – Jakob S
  Nov 3 '11 at 10:29
  
  
  

  
  
  
  


• 
  
  
  

  
  6
  

  
  
  
  
  
  

  
  
  If you use that patch, I'd rename it to numeric?, to stay in line with ruby naming conventions (Numeric classes inherit from Numeric, is_ prefixes are javaish).
  
  – Konrad Reiche
  Jun 24 '12 at 18:34
  

  
  
  
  


• 
  
  
  

  
  9
  

  
  
  
  
  
  

  
  
  Not really relevant to the original question, but I'd probably put the code in lib/core_ext/string.rb.
  
  – Jakob S
  Aug 7 '12 at 8:48
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I don't think the is_number?(string) bit works Ruby 1.9. Maybe that is part of Rails or 1.8? String.is_a?(Numeric) works. See also stackoverflow.com/questions/2095493/….
  
  – Ross Attrill
  Jun 16 '14 at 7:10
  
  
  

  
  
  
  

2

2

This is a bad idea. "330.346.11".to_f # => 330.346

– epochwolf
Nov 2 '11 at 23:15

This is a bad idea. "330.346.11".to_f # => 330.346

– epochwolf
Nov 2 '11 at 23:15

11

11

There is no to_f in the above, and Float() doesn't exhibit that behavior: Float("330.346.11") raises ArgumentError: invalid value for Float(): "330.346.11"

– Jakob S
Nov 3 '11 at 10:29

There is no to_f in the above, and Float() doesn't exhibit that behavior: Float("330.346.11") raises ArgumentError: invalid value for Float(): "330.346.11"

– Jakob S
Nov 3 '11 at 10:29

6

6

If you use that patch, I'd rename it to numeric?, to stay in line with ruby naming conventions (Numeric classes inherit from Numeric, is_ prefixes are javaish).

– Konrad Reiche
Jun 24 '12 at 18:34

If you use that patch, I'd rename it to numeric?, to stay in line with ruby naming conventions (Numeric classes inherit from Numeric, is_ prefixes are javaish).

– Konrad Reiche
Jun 24 '12 at 18:34

9

9

Not really relevant to the original question, but I'd probably put the code in lib/core_ext/string.rb.

– Jakob S
Aug 7 '12 at 8:48

Not really relevant to the original question, but I'd probably put the code in lib/core_ext/string.rb.

– Jakob S
Aug 7 '12 at 8:48

1

1

I don't think the is_number?(string) bit works Ruby 1.9. Maybe that is part of Rails or 1.8? String.is_a?(Numeric) works. See also stackoverflow.com/questions/2095493/….

– Ross Attrill
Jun 16 '14 at 7:10

I don't think the is_number?(string) bit works Ruby 1.9. Maybe that is part of Rails or 1.8? String.is_a?(Numeric) works. See also stackoverflow.com/questions/2095493/….

– Ross Attrill
Jun 16 '14 at 7:10

 | 
show 7 more comments

29

class String

  def numeric?

    return true if self =~ /Ad+Z/

    true if Float(self) rescue false

  end

end  



p "1".numeric?  # => true

p "1.2".numeric? # => true

p "5.4e-29".numeric? # => true

p "12e20".numeric? # true

p "1a".numeric? # => false

p "1.2.3.4".numeric? # => false

share|improve this answer

edited May 1 '15 at 20:40

Marius Butuc

10.2k1868107

answered Jul 25 '12 at 16:02

hipertrackerhipertracker

2,1182212

• 
  
  
  

  
  11
  

  
  
  
  
  
  

  
  
  /^d+$/ is not a safe regexp in Ruby, /Ad+Z/ is. (e.g. "42nsome text" would return true)
  
  – Timothee A
  Sep 1 '14 at 15:18
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  To clarify on @TimotheeA's comment, it is safe to use /^d+$/ if dealing with lines but in this case it's about beginning and end of a string, thus /Ad+Z/.
  
  – Julio
  Oct 9 '14 at 20:09
  
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Shouldn't answers be edited to change the actual answer BY the responder? changing the answer in an edit if you're not the responder seems...possibly underhanded and should be out of bounds.
  
  – jaydel
  Jul 20 '16 at 15:43
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Where should I put these codes?
  
  – zx1986
  Jul 7 '17 at 4:10
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Z allows to have n at the end of the string, so "123n" will pass validation, regardless that it's not fully numeric. But if you use z then it will be more correct regexp: /Ad+z/
  
  – SunnyMagadan
  Aug 14 '17 at 9:14
  

  
  
  
  

add a comment | 

29

class String

  def numeric?

    return true if self =~ /Ad+Z/

    true if Float(self) rescue false

  end

end  



p "1".numeric?  # => true

p "1.2".numeric? # => true

p "5.4e-29".numeric? # => true

p "12e20".numeric? # true

p "1a".numeric? # => false

p "1.2.3.4".numeric? # => false

share|improve this answer

edited May 1 '15 at 20:40

Marius Butuc

10.2k1868107

answered Jul 25 '12 at 16:02

hipertrackerhipertracker

2,1182212

• 
  
  
  

  
  11
  

  
  
  
  
  
  

  
  
  /^d+$/ is not a safe regexp in Ruby, /Ad+Z/ is. (e.g. "42nsome text" would return true)
  
  – Timothee A
  Sep 1 '14 at 15:18
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  To clarify on @TimotheeA's comment, it is safe to use /^d+$/ if dealing with lines but in this case it's about beginning and end of a string, thus /Ad+Z/.
  
  – Julio
  Oct 9 '14 at 20:09
  
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Shouldn't answers be edited to change the actual answer BY the responder? changing the answer in an edit if you're not the responder seems...possibly underhanded and should be out of bounds.
  
  – jaydel
  Jul 20 '16 at 15:43
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Where should I put these codes?
  
  – zx1986
  Jul 7 '17 at 4:10
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Z allows to have n at the end of the string, so "123n" will pass validation, regardless that it's not fully numeric. But if you use z then it will be more correct regexp: /Ad+z/
  
  – SunnyMagadan
  Aug 14 '17 at 9:14
  

  
  
  
  

add a comment | 

29

29

29

class String

  def numeric?

    return true if self =~ /Ad+Z/

    true if Float(self) rescue false

  end

end  



p "1".numeric?  # => true

p "1.2".numeric? # => true

p "5.4e-29".numeric? # => true

p "12e20".numeric? # true

p "1a".numeric? # => false

p "1.2.3.4".numeric? # => false

share|improve this answer

edited May 1 '15 at 20:40

Marius Butuc

10.2k1868107

answered Jul 25 '12 at 16:02

hipertrackerhipertracker

2,1182212

class String

  def numeric?

    return true if self =~ /Ad+Z/

    true if Float(self) rescue false

  end

end  



p "1".numeric?  # => true

p "1.2".numeric? # => true

p "5.4e-29".numeric? # => true

p "12e20".numeric? # true

p "1a".numeric? # => false

p "1.2.3.4".numeric? # => false

share|improve this answer

edited May 1 '15 at 20:40

Marius Butuc

10.2k1868107

answered Jul 25 '12 at 16:02

hipertrackerhipertracker

2,1182212

share|improve this answer

share|improve this answer

edited May 1 '15 at 20:40

Marius Butuc

10.2k1868107

edited May 1 '15 at 20:40

Marius Butuc

10.2k1868107

edited May 1 '15 at 20:40

Marius Butuc

10.2k1868107

10.2k1868107

answered Jul 25 '12 at 16:02

hipertrackerhipertracker

2,1182212

answered Jul 25 '12 at 16:02

hipertrackerhipertracker

2,1182212

answered Jul 25 '12 at 16:02

hipertrackerhipertracker

2,1182212

2,1182212

• 
  
  
  

  
  11
  

  
  
  
  
  
  

  
  
  /^d+$/ is not a safe regexp in Ruby, /Ad+Z/ is. (e.g. "42nsome text" would return true)
  
  – Timothee A
  Sep 1 '14 at 15:18
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  To clarify on @TimotheeA's comment, it is safe to use /^d+$/ if dealing with lines but in this case it's about beginning and end of a string, thus /Ad+Z/.
  
  – Julio
  Oct 9 '14 at 20:09
  
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Shouldn't answers be edited to change the actual answer BY the responder? changing the answer in an edit if you're not the responder seems...possibly underhanded and should be out of bounds.
  
  – jaydel
  Jul 20 '16 at 15:43
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Where should I put these codes?
  
  – zx1986
  Jul 7 '17 at 4:10
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Z allows to have n at the end of the string, so "123n" will pass validation, regardless that it's not fully numeric. But if you use z then it will be more correct regexp: /Ad+z/
  
  – SunnyMagadan
  Aug 14 '17 at 9:14
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  11
  

  
  
  
  
  
  

  
  
  /^d+$/ is not a safe regexp in Ruby, /Ad+Z/ is. (e.g. "42nsome text" would return true)
  
  – Timothee A
  Sep 1 '14 at 15:18
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  To clarify on @TimotheeA's comment, it is safe to use /^d+$/ if dealing with lines but in this case it's about beginning and end of a string, thus /Ad+Z/.
  
  – Julio
  Oct 9 '14 at 20:09
  
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Shouldn't answers be edited to change the actual answer BY the responder? changing the answer in an edit if you're not the responder seems...possibly underhanded and should be out of bounds.
  
  – jaydel
  Jul 20 '16 at 15:43
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Where should I put these codes?
  
  – zx1986
  Jul 7 '17 at 4:10
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Z allows to have n at the end of the string, so "123n" will pass validation, regardless that it's not fully numeric. But if you use z then it will be more correct regexp: /Ad+z/
  
  – SunnyMagadan
  Aug 14 '17 at 9:14
  

  
  
  
  

11

11

/^d+$/ is not a safe regexp in Ruby, /Ad+Z/ is. (e.g. "42nsome text" would return true)

– Timothee A
Sep 1 '14 at 15:18

/^d+$/ is not a safe regexp in Ruby, /Ad+Z/ is. (e.g. "42nsome text" would return true)

– Timothee A
Sep 1 '14 at 15:18

To clarify on @TimotheeA's comment, it is safe to use /^d+$/ if dealing with lines but in this case it's about beginning and end of a string, thus /Ad+Z/.

– Julio
Oct 9 '14 at 20:09

To clarify on @TimotheeA's comment, it is safe to use /^d+$/ if dealing with lines but in this case it's about beginning and end of a string, thus /Ad+Z/.

– Julio
Oct 9 '14 at 20:09

1

1

Shouldn't answers be edited to change the actual answer BY the responder? changing the answer in an edit if you're not the responder seems...possibly underhanded and should be out of bounds.

– jaydel
Jul 20 '16 at 15:43

Shouldn't answers be edited to change the actual answer BY the responder? changing the answer in an edit if you're not the responder seems...possibly underhanded and should be out of bounds.

– jaydel
Jul 20 '16 at 15:43

Where should I put these codes?

– zx1986
Jul 7 '17 at 4:10

Where should I put these codes?

– zx1986
Jul 7 '17 at 4:10

2

2

Z allows to have n at the end of the string, so "123n" will pass validation, regardless that it's not fully numeric. But if you use z then it will be more correct regexp: /Ad+z/

– SunnyMagadan
Aug 14 '17 at 9:14

Z allows to have n at the end of the string, so "123n" will pass validation, regardless that it's not fully numeric. But if you use z then it will be more correct regexp: /Ad+z/

– SunnyMagadan
Aug 14 '17 at 9:14

add a comment | 

26

Here's a benchmark for common ways to address this problem. Note which one you should use probably depends on the ratio of false cases expected.

1. If they are relatively uncommon casting is definitely fastest.


2. If false cases are common and you are just checking for ints, comparison vs a transformed state is a good option.


3. If false cases are common and you are checking floats, regexp is probably the way to go

If performance doesn't matter use what you like. :-)

Integer checking details:

# 1.9.3-p448

#

# Calculating -------------------------------------

#                 cast     57485 i/100ms

#            cast fail      5549 i/100ms

#                 to_s     47509 i/100ms

#            to_s fail     50573 i/100ms

#               regexp     45187 i/100ms

#          regexp fail     42566 i/100ms

# -------------------------------------------------

#                 cast  2353703.4 (±4.9%) i/s -   11726940 in   4.998270s

#            cast fail    65590.2 (±4.6%) i/s -     327391 in   5.003511s

#                 to_s  1420892.0 (±6.8%) i/s -    7078841 in   5.011462s

#            to_s fail  1717948.8 (±6.0%) i/s -    8546837 in   4.998672s

#               regexp  1525729.9 (±7.0%) i/s -    7591416 in   5.007105s

#          regexp fail  1154461.1 (±5.5%) i/s -    5788976 in   5.035311s



require 'benchmark/ips'



int = '220000'

bad_int = '22.to.2'



Benchmark.ips do |x|

  x.report('cast') do

    Integer(int) rescue false

  end



  x.report('cast fail') do

    Integer(bad_int) rescue false

  end



  x.report('to_s') do

    int.to_i.to_s == int

  end



  x.report('to_s fail') do

    bad_int.to_i.to_s == bad_int

  end



  x.report('regexp') do

    int =~ /^d+$/

  end



  x.report('regexp fail') do

    bad_int =~ /^d+$/

  end

end

Float checking details:

# 1.9.3-p448

#

# Calculating -------------------------------------

#                 cast     47430 i/100ms

#            cast fail      5023 i/100ms

#                 to_s     27435 i/100ms

#            to_s fail     29609 i/100ms

#               regexp     37620 i/100ms

#          regexp fail     32557 i/100ms

# -------------------------------------------------

#                 cast  2283762.5 (±6.8%) i/s -   11383200 in   5.012934s

#            cast fail    63108.8 (±6.7%) i/s -     316449 in   5.038518s

#                 to_s   593069.3 (±8.8%) i/s -    2962980 in   5.042459s

#            to_s fail   857217.1 (±10.0%) i/s -    4263696 in   5.033024s

#               regexp  1383194.8 (±6.7%) i/s -    6884460 in   5.008275s

#          regexp fail   723390.2 (±5.8%) i/s -    3613827 in   5.016494s



require 'benchmark/ips'



float = '12.2312'

bad_float = '22.to.2'



Benchmark.ips do |x|

  x.report('cast') do

    Float(float) rescue false

  end



  x.report('cast fail') do

    Float(bad_float) rescue false

  end



  x.report('to_s') do

    float.to_f.to_s == float

  end



  x.report('to_s fail') do

    bad_float.to_f.to_s == bad_float

  end



  x.report('regexp') do

    float =~ /^[-+]?[0-9]*.?[0-9]+$/

  end



  x.report('regexp fail') do

    bad_float =~ /^[-+]?[0-9]*.?[0-9]+$/

  end

end

share|improve this answer

answered Nov 8 '13 at 1:22

Matt SandersMatt Sanders

4,0772133

add a comment | 

26

Here's a benchmark for common ways to address this problem. Note which one you should use probably depends on the ratio of false cases expected.

1. If they are relatively uncommon casting is definitely fastest.


2. If false cases are common and you are just checking for ints, comparison vs a transformed state is a good option.


3. If false cases are common and you are checking floats, regexp is probably the way to go

If performance doesn't matter use what you like. :-)

Integer checking details:

# 1.9.3-p448

#

# Calculating -------------------------------------

#                 cast     57485 i/100ms

#            cast fail      5549 i/100ms

#                 to_s     47509 i/100ms

#            to_s fail     50573 i/100ms

#               regexp     45187 i/100ms

#          regexp fail     42566 i/100ms

# -------------------------------------------------

#                 cast  2353703.4 (±4.9%) i/s -   11726940 in   4.998270s

#            cast fail    65590.2 (±4.6%) i/s -     327391 in   5.003511s

#                 to_s  1420892.0 (±6.8%) i/s -    7078841 in   5.011462s

#            to_s fail  1717948.8 (±6.0%) i/s -    8546837 in   4.998672s

#               regexp  1525729.9 (±7.0%) i/s -    7591416 in   5.007105s

#          regexp fail  1154461.1 (±5.5%) i/s -    5788976 in   5.035311s



require 'benchmark/ips'



int = '220000'

bad_int = '22.to.2'



Benchmark.ips do |x|

  x.report('cast') do

    Integer(int) rescue false

  end



  x.report('cast fail') do

    Integer(bad_int) rescue false

  end



  x.report('to_s') do

    int.to_i.to_s == int

  end



  x.report('to_s fail') do

    bad_int.to_i.to_s == bad_int

  end



  x.report('regexp') do

    int =~ /^d+$/

  end



  x.report('regexp fail') do

    bad_int =~ /^d+$/

  end

end

Float checking details:

# 1.9.3-p448

#

# Calculating -------------------------------------

#                 cast     47430 i/100ms

#            cast fail      5023 i/100ms

#                 to_s     27435 i/100ms

#            to_s fail     29609 i/100ms

#               regexp     37620 i/100ms

#          regexp fail     32557 i/100ms

# -------------------------------------------------

#                 cast  2283762.5 (±6.8%) i/s -   11383200 in   5.012934s

#            cast fail    63108.8 (±6.7%) i/s -     316449 in   5.038518s

#                 to_s   593069.3 (±8.8%) i/s -    2962980 in   5.042459s

#            to_s fail   857217.1 (±10.0%) i/s -    4263696 in   5.033024s

#               regexp  1383194.8 (±6.7%) i/s -    6884460 in   5.008275s

#          regexp fail   723390.2 (±5.8%) i/s -    3613827 in   5.016494s



require 'benchmark/ips'



float = '12.2312'

bad_float = '22.to.2'



Benchmark.ips do |x|

  x.report('cast') do

    Float(float) rescue false

  end



  x.report('cast fail') do

    Float(bad_float) rescue false

  end



  x.report('to_s') do

    float.to_f.to_s == float

  end



  x.report('to_s fail') do

    bad_float.to_f.to_s == bad_float

  end



  x.report('regexp') do

    float =~ /^[-+]?[0-9]*.?[0-9]+$/

  end



  x.report('regexp fail') do

    bad_float =~ /^[-+]?[0-9]*.?[0-9]+$/

  end

end

share|improve this answer

answered Nov 8 '13 at 1:22

Matt SandersMatt Sanders

4,0772133

add a comment | 

26

26

26

Here's a benchmark for common ways to address this problem. Note which one you should use probably depends on the ratio of false cases expected.

1. If they are relatively uncommon casting is definitely fastest.


2. If false cases are common and you are just checking for ints, comparison vs a transformed state is a good option.


3. If false cases are common and you are checking floats, regexp is probably the way to go

If performance doesn't matter use what you like. :-)

Integer checking details:

# 1.9.3-p448

#

# Calculating -------------------------------------

#                 cast     57485 i/100ms

#            cast fail      5549 i/100ms

#                 to_s     47509 i/100ms

#            to_s fail     50573 i/100ms

#               regexp     45187 i/100ms

#          regexp fail     42566 i/100ms

# -------------------------------------------------

#                 cast  2353703.4 (±4.9%) i/s -   11726940 in   4.998270s

#            cast fail    65590.2 (±4.6%) i/s -     327391 in   5.003511s

#                 to_s  1420892.0 (±6.8%) i/s -    7078841 in   5.011462s

#            to_s fail  1717948.8 (±6.0%) i/s -    8546837 in   4.998672s

#               regexp  1525729.9 (±7.0%) i/s -    7591416 in   5.007105s

#          regexp fail  1154461.1 (±5.5%) i/s -    5788976 in   5.035311s



require 'benchmark/ips'



int = '220000'

bad_int = '22.to.2'



Benchmark.ips do |x|

  x.report('cast') do

    Integer(int) rescue false

  end



  x.report('cast fail') do

    Integer(bad_int) rescue false

  end



  x.report('to_s') do

    int.to_i.to_s == int

  end



  x.report('to_s fail') do

    bad_int.to_i.to_s == bad_int

  end



  x.report('regexp') do

    int =~ /^d+$/

  end



  x.report('regexp fail') do

    bad_int =~ /^d+$/

  end

end

Float checking details:

# 1.9.3-p448

#

# Calculating -------------------------------------

#                 cast     47430 i/100ms

#            cast fail      5023 i/100ms

#                 to_s     27435 i/100ms

#            to_s fail     29609 i/100ms

#               regexp     37620 i/100ms

#          regexp fail     32557 i/100ms

# -------------------------------------------------

#                 cast  2283762.5 (±6.8%) i/s -   11383200 in   5.012934s

#            cast fail    63108.8 (±6.7%) i/s -     316449 in   5.038518s

#                 to_s   593069.3 (±8.8%) i/s -    2962980 in   5.042459s

#            to_s fail   857217.1 (±10.0%) i/s -    4263696 in   5.033024s

#               regexp  1383194.8 (±6.7%) i/s -    6884460 in   5.008275s

#          regexp fail   723390.2 (±5.8%) i/s -    3613827 in   5.016494s



require 'benchmark/ips'



float = '12.2312'

bad_float = '22.to.2'



Benchmark.ips do |x|

  x.report('cast') do

    Float(float) rescue false

  end



  x.report('cast fail') do

    Float(bad_float) rescue false

  end



  x.report('to_s') do

    float.to_f.to_s == float

  end



  x.report('to_s fail') do

    bad_float.to_f.to_s == bad_float

  end



  x.report('regexp') do

    float =~ /^[-+]?[0-9]*.?[0-9]+$/

  end



  x.report('regexp fail') do

    bad_float =~ /^[-+]?[0-9]*.?[0-9]+$/

  end

end

share|improve this answer

answered Nov 8 '13 at 1:22

Matt SandersMatt Sanders

4,0772133

Here's a benchmark for common ways to address this problem. Note which one you should use probably depends on the ratio of false cases expected.

1. If they are relatively uncommon casting is definitely fastest.


2. If false cases are common and you are just checking for ints, comparison vs a transformed state is a good option.


3. If false cases are common and you are checking floats, regexp is probably the way to go

If performance doesn't matter use what you like. :-)

Integer checking details:

# 1.9.3-p448

#

# Calculating -------------------------------------

#                 cast     57485 i/100ms

#            cast fail      5549 i/100ms

#                 to_s     47509 i/100ms

#            to_s fail     50573 i/100ms

#               regexp     45187 i/100ms

#          regexp fail     42566 i/100ms

# -------------------------------------------------

#                 cast  2353703.4 (±4.9%) i/s -   11726940 in   4.998270s

#            cast fail    65590.2 (±4.6%) i/s -     327391 in   5.003511s

#                 to_s  1420892.0 (±6.8%) i/s -    7078841 in   5.011462s

#            to_s fail  1717948.8 (±6.0%) i/s -    8546837 in   4.998672s

#               regexp  1525729.9 (±7.0%) i/s -    7591416 in   5.007105s

#          regexp fail  1154461.1 (±5.5%) i/s -    5788976 in   5.035311s



require 'benchmark/ips'



int = '220000'

bad_int = '22.to.2'



Benchmark.ips do |x|

  x.report('cast') do

    Integer(int) rescue false

  end



  x.report('cast fail') do

    Integer(bad_int) rescue false

  end



  x.report('to_s') do

    int.to_i.to_s == int

  end



  x.report('to_s fail') do

    bad_int.to_i.to_s == bad_int

  end



  x.report('regexp') do

    int =~ /^d+$/

  end



  x.report('regexp fail') do

    bad_int =~ /^d+$/

  end

end

Float checking details:

# 1.9.3-p448

#

# Calculating -------------------------------------

#                 cast     47430 i/100ms

#            cast fail      5023 i/100ms

#                 to_s     27435 i/100ms

#            to_s fail     29609 i/100ms

#               regexp     37620 i/100ms

#          regexp fail     32557 i/100ms

# -------------------------------------------------

#                 cast  2283762.5 (±6.8%) i/s -   11383200 in   5.012934s

#            cast fail    63108.8 (±6.7%) i/s -     316449 in   5.038518s

#                 to_s   593069.3 (±8.8%) i/s -    2962980 in   5.042459s

#            to_s fail   857217.1 (±10.0%) i/s -    4263696 in   5.033024s

#               regexp  1383194.8 (±6.7%) i/s -    6884460 in   5.008275s

#          regexp fail   723390.2 (±5.8%) i/s -    3613827 in   5.016494s



require 'benchmark/ips'



float = '12.2312'

bad_float = '22.to.2'



Benchmark.ips do |x|

  x.report('cast') do

    Float(float) rescue false

  end



  x.report('cast fail') do

    Float(bad_float) rescue false

  end



  x.report('to_s') do

    float.to_f.to_s == float

  end



  x.report('to_s fail') do

    bad_float.to_f.to_s == bad_float

  end



  x.report('regexp') do

    float =~ /^[-+]?[0-9]*.?[0-9]+$/

  end



  x.report('regexp fail') do

    bad_float =~ /^[-+]?[0-9]*.?[0-9]+$/

  end

end

share|improve this answer

answered Nov 8 '13 at 1:22

Matt SandersMatt Sanders

4,0772133

share|improve this answer

share|improve this answer

answered Nov 8 '13 at 1:22

Matt SandersMatt Sanders

4,0772133

answered Nov 8 '13 at 1:22

Matt SandersMatt Sanders

4,0772133

answered Nov 8 '13 at 1:22

Matt SandersMatt Sanders

4,0772133

4,0772133

add a comment | 

add a comment | 

14

Relying on the raised exception is not the fastest, readable nor reliable solution.

I'd do the following :

my_string.should =~ /^[0-9]+$/

share|improve this answer

answered Apr 14 '11 at 10:20

Damien MATHIEUDamien MATHIEU

24k126586

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  This only works for positive integers, however. Values like '-1', '0.0', or '1_000' all return false even though they are valid numeric values. You're looking at something like /^[-.0-9]+$/, but that erroneously accepts '--'.
  
  – Jakob S
  Apr 14 '11 at 11:03
  

  
  
  
  


• 
  
  
  

  
  10
  

  
  
  
  
  
  

  
  
  From Rails 'validates_numericality_of': raw_value.to_s =~ /A[+-]?d+Z/
  
  – Morten
  Aug 17 '12 at 20:09
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  NoMethodError: undefined method `should' for "asd":String
  
  – sergserg
  Oct 9 '14 at 22:08
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In the latest rspec, this becomes expect(my_string).to match(/^[0-9]+$/)
  
  – Damien MATHIEU
  Oct 10 '14 at 8:55
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I like: my_string =~ /A-?(d+)?.?d+Z/ it lets you do '.1', '-0.1', or '12' but not '' or '-' or '.'
  
  – Josh
  Sep 2 '16 at 0:05
  

  
  
  
  

 | 
show 1 more comment

14

Relying on the raised exception is not the fastest, readable nor reliable solution.

I'd do the following :

my_string.should =~ /^[0-9]+$/

share|improve this answer

answered Apr 14 '11 at 10:20

Damien MATHIEUDamien MATHIEU

24k126586

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  This only works for positive integers, however. Values like '-1', '0.0', or '1_000' all return false even though they are valid numeric values. You're looking at something like /^[-.0-9]+$/, but that erroneously accepts '--'.
  
  – Jakob S
  Apr 14 '11 at 11:03
  

  
  
  
  


• 
  
  
  

  
  10
  

  
  
  
  
  
  

  
  
  From Rails 'validates_numericality_of': raw_value.to_s =~ /A[+-]?d+Z/
  
  – Morten
  Aug 17 '12 at 20:09
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  NoMethodError: undefined method `should' for "asd":String
  
  – sergserg
  Oct 9 '14 at 22:08
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In the latest rspec, this becomes expect(my_string).to match(/^[0-9]+$/)
  
  – Damien MATHIEU
  Oct 10 '14 at 8:55
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I like: my_string =~ /A-?(d+)?.?d+Z/ it lets you do '.1', '-0.1', or '12' but not '' or '-' or '.'
  
  – Josh
  Sep 2 '16 at 0:05
  

  
  
  
  

 | 
show 1 more comment

14

14

14

Relying on the raised exception is not the fastest, readable nor reliable solution.

I'd do the following :

my_string.should =~ /^[0-9]+$/

share|improve this answer

answered Apr 14 '11 at 10:20

Damien MATHIEUDamien MATHIEU

24k126586

Relying on the raised exception is not the fastest, readable nor reliable solution.

I'd do the following :

my_string.should =~ /^[0-9]+$/

share|improve this answer

answered Apr 14 '11 at 10:20

Damien MATHIEUDamien MATHIEU

24k126586

share|improve this answer

share|improve this answer

answered Apr 14 '11 at 10:20

Damien MATHIEUDamien MATHIEU

24k126586

answered Apr 14 '11 at 10:20

Damien MATHIEUDamien MATHIEU

24k126586

answered Apr 14 '11 at 10:20

Damien MATHIEUDamien MATHIEU

24k126586

24k126586

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  This only works for positive integers, however. Values like '-1', '0.0', or '1_000' all return false even though they are valid numeric values. You're looking at something like /^[-.0-9]+$/, but that erroneously accepts '--'.
  
  – Jakob S
  Apr 14 '11 at 11:03
  

  
  
  
  


• 
  
  
  

  
  10
  

  
  
  
  
  
  

  
  
  From Rails 'validates_numericality_of': raw_value.to_s =~ /A[+-]?d+Z/
  
  – Morten
  Aug 17 '12 at 20:09
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  NoMethodError: undefined method `should' for "asd":String
  
  – sergserg
  Oct 9 '14 at 22:08
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In the latest rspec, this becomes expect(my_string).to match(/^[0-9]+$/)
  
  – Damien MATHIEU
  Oct 10 '14 at 8:55
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I like: my_string =~ /A-?(d+)?.?d+Z/ it lets you do '.1', '-0.1', or '12' but not '' or '-' or '.'
  
  – Josh
  Sep 2 '16 at 0:05
  

  
  
  
  

 | 
show 1 more comment

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  This only works for positive integers, however. Values like '-1', '0.0', or '1_000' all return false even though they are valid numeric values. You're looking at something like /^[-.0-9]+$/, but that erroneously accepts '--'.
  
  – Jakob S
  Apr 14 '11 at 11:03
  

  
  
  
  


• 
  
  
  

  
  10
  

  
  
  
  
  
  

  
  
  From Rails 'validates_numericality_of': raw_value.to_s =~ /A[+-]?d+Z/
  
  – Morten
  Aug 17 '12 at 20:09
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  NoMethodError: undefined method `should' for "asd":String
  
  – sergserg
  Oct 9 '14 at 22:08
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In the latest rspec, this becomes expect(my_string).to match(/^[0-9]+$/)
  
  – Damien MATHIEU
  Oct 10 '14 at 8:55
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I like: my_string =~ /A-?(d+)?.?d+Z/ it lets you do '.1', '-0.1', or '12' but not '' or '-' or '.'
  
  – Josh
  Sep 2 '16 at 0:05
  

  
  
  
  

1

1

This only works for positive integers, however. Values like '-1', '0.0', or '1_000' all return false even though they are valid numeric values. You're looking at something like /^[-.0-9]+$/, but that erroneously accepts '--'.

– Jakob S
Apr 14 '11 at 11:03

This only works for positive integers, however. Values like '-1', '0.0', or '1_000' all return false even though they are valid numeric values. You're looking at something like /^[-.0-9]+$/, but that erroneously accepts '--'.

– Jakob S
Apr 14 '11 at 11:03

10

10

From Rails 'validates_numericality_of': raw_value.to_s =~ /A[+-]?d+Z/

– Morten
Aug 17 '12 at 20:09

From Rails 'validates_numericality_of': raw_value.to_s =~ /A[+-]?d+Z/

– Morten
Aug 17 '12 at 20:09

NoMethodError: undefined method `should' for "asd":String

– sergserg
Oct 9 '14 at 22:08

NoMethodError: undefined method `should' for "asd":String

– sergserg
Oct 9 '14 at 22:08

In the latest rspec, this becomes expect(my_string).to match(/^[0-9]+$/)

– Damien MATHIEU
Oct 10 '14 at 8:55

In the latest rspec, this becomes expect(my_string).to match(/^[0-9]+$/)

– Damien MATHIEU
Oct 10 '14 at 8:55

I like: my_string =~ /A-?(d+)?.?d+Z/ it lets you do '.1', '-0.1', or '12' but not '' or '-' or '.'

– Josh
Sep 2 '16 at 0:05

I like: my_string =~ /A-?(d+)?.?d+Z/ it lets you do '.1', '-0.1', or '12' but not '' or '-' or '.'

– Josh
Sep 2 '16 at 0:05

 | 
show 1 more comment

6

no you're just using it wrong. your is_number? has an argument. you called it without the argument

you should be doing is_number?(mystring)

share|improve this answer

edited Apr 14 '11 at 10:22

answered Apr 14 '11 at 9:58

corrodedcorroded

15k1772128

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Based on the is_number? method in the question, using is_a? is not giving the correct answer. If mystring is indeed a String, mystring.is_a?(Integer) will always be false. It looks like he wants a result like is_number?("12.4") #=> true
  
  – Jakob S
  Apr 14 '11 at 10:15
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  mmm good point, lemme update that
  
  – corroded
  Apr 14 '11 at 10:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Jakob S is correct. mystring is indeed always a string, but may be comprise of just numbers. perhaps my question should have been is_numeric? so as not to confuse the datatype
  
  – Jamie Buchanan
  Apr 14 '11 at 10:23
  

  
  
  
  

add a comment | 

6

no you're just using it wrong. your is_number? has an argument. you called it without the argument

you should be doing is_number?(mystring)

share|improve this answer

edited Apr 14 '11 at 10:22

answered Apr 14 '11 at 9:58

corrodedcorroded

15k1772128

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Based on the is_number? method in the question, using is_a? is not giving the correct answer. If mystring is indeed a String, mystring.is_a?(Integer) will always be false. It looks like he wants a result like is_number?("12.4") #=> true
  
  – Jakob S
  Apr 14 '11 at 10:15
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  mmm good point, lemme update that
  
  – corroded
  Apr 14 '11 at 10:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Jakob S is correct. mystring is indeed always a string, but may be comprise of just numbers. perhaps my question should have been is_numeric? so as not to confuse the datatype
  
  – Jamie Buchanan
  Apr 14 '11 at 10:23
  

  
  
  
  

add a comment | 

6

6

6

no you're just using it wrong. your is_number? has an argument. you called it without the argument

you should be doing is_number?(mystring)

share|improve this answer

edited Apr 14 '11 at 10:22

answered Apr 14 '11 at 9:58

corrodedcorroded

15k1772128

no you're just using it wrong. your is_number? has an argument. you called it without the argument

you should be doing is_number?(mystring)

share|improve this answer

edited Apr 14 '11 at 10:22

answered Apr 14 '11 at 9:58

corrodedcorroded

15k1772128

share|improve this answer

share|improve this answer

edited Apr 14 '11 at 10:22

edited Apr 14 '11 at 10:22

edited Apr 14 '11 at 10:22

answered Apr 14 '11 at 9:58

corrodedcorroded

15k1772128

answered Apr 14 '11 at 9:58

corrodedcorroded

15k1772128

answered Apr 14 '11 at 9:58

corrodedcorroded

15k1772128

15k1772128

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Based on the is_number? method in the question, using is_a? is not giving the correct answer. If mystring is indeed a String, mystring.is_a?(Integer) will always be false. It looks like he wants a result like is_number?("12.4") #=> true
  
  – Jakob S
  Apr 14 '11 at 10:15
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  mmm good point, lemme update that
  
  – corroded
  Apr 14 '11 at 10:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Jakob S is correct. mystring is indeed always a string, but may be comprise of just numbers. perhaps my question should have been is_numeric? so as not to confuse the datatype
  
  – Jamie Buchanan
  Apr 14 '11 at 10:23
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Based on the is_number? method in the question, using is_a? is not giving the correct answer. If mystring is indeed a String, mystring.is_a?(Integer) will always be false. It looks like he wants a result like is_number?("12.4") #=> true
  
  – Jakob S
  Apr 14 '11 at 10:15
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  mmm good point, lemme update that
  
  – corroded
  Apr 14 '11 at 10:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Jakob S is correct. mystring is indeed always a string, but may be comprise of just numbers. perhaps my question should have been is_numeric? so as not to confuse the datatype
  
  – Jamie Buchanan
  Apr 14 '11 at 10:23
  

  
  
  
  

Based on the is_number? method in the question, using is_a? is not giving the correct answer. If mystring is indeed a String, mystring.is_a?(Integer) will always be false. It looks like he wants a result like is_number?("12.4") #=> true

– Jakob S
Apr 14 '11 at 10:15

Based on the is_number? method in the question, using is_a? is not giving the correct answer. If mystring is indeed a String, mystring.is_a?(Integer) will always be false. It looks like he wants a result like is_number?("12.4") #=> true

– Jakob S
Apr 14 '11 at 10:15

mmm good point, lemme update that

– corroded
Apr 14 '11 at 10:20

mmm good point, lemme update that

– corroded
Apr 14 '11 at 10:20

Jakob S is correct. mystring is indeed always a string, but may be comprise of just numbers. perhaps my question should have been is_numeric? so as not to confuse the datatype

– Jamie Buchanan
Apr 14 '11 at 10:23

Jakob S is correct. mystring is indeed always a string, but may be comprise of just numbers. perhaps my question should have been is_numeric? so as not to confuse the datatype

– Jamie Buchanan
Apr 14 '11 at 10:23

add a comment | 

5

Tl;dr: Use a regex approach. It is 39x faster than the rescue approach in the accepted answer and also handles cases like "1,000"

def regex_is_number? string

  no_commas =  string.gsub(',', '')

  matches = no_commas.match(/-?d+(?:.d+)?/)

  if !matches.nil? && matches.size == 1 && matches[0] == no_commas

    true

  else

    false

  end

end

--

The accepted answer by @Jakob S works for the most part, but catching exceptions can be really slow. In addition, the rescue approach fails on a string like "1,000".

Let's define the methods:

def rescue_is_number? string

  true if Float(string) rescue false

end



def regex_is_number? string

  no_commas =  string.gsub(',', '')

  matches = no_commas.match(/-?d+(?:.d+)?/)

  if !matches.nil? && matches.size == 1 && matches[0] == no_commas

    true

  else

    false

  end

end

And now some test cases:

test_cases = {

  true => ["5.5", "23", "-123", "1,234,123"],

  false => ["hello", "99designs", "(123)456-7890"]

}

And a little code to run the test cases:

test_cases.each do |expected_answer, cases|

  cases.each do |test_case|

    if rescue_is_number?(test_case) != expected_answer

      puts "**rescue_is_number? got #{test_case} wrong**"

    else

      puts "rescue_is_number? got #{test_case} right"

    end



    if regex_is_number?(test_case) != expected_answer

      puts "**regex_is_number? got #{test_case} wrong**"

    else

      puts "regex_is_number? got #{test_case} right"

    end  

  end

end

Here is the output of the test cases:

rescue_is_number? got 5.5 right

regex_is_number? got 5.5 right

rescue_is_number? got 23 right

regex_is_number? got 23 right

rescue_is_number? got -123 right

regex_is_number? got -123 right

**rescue_is_number? got 1,234,123 wrong**

regex_is_number? got 1,234,123 right

rescue_is_number? got hello right

regex_is_number? got hello right

rescue_is_number? got 99designs right

regex_is_number? got 99designs right

rescue_is_number? got (123)456-7890 right

regex_is_number? got (123)456-7890 right

Time to do some performance benchmarks:

Benchmark.ips do |x|



  x.report("rescue") { test_cases.values.flatten.each { |c| rescue_is_number? c } }

  x.report("regex") { test_cases.values.flatten.each { |c| regex_is_number? c } }



  x.compare!

end

And the results:

Calculating -------------------------------------

              rescue   128.000  i/100ms

               regex     4.649k i/100ms

-------------------------------------------------

              rescue      1.348k (±16.8%) i/s -      6.656k

               regex     52.113k (± 7.8%) i/s -    260.344k



Comparison:

               regex:    52113.3 i/s

              rescue:     1347.5 i/s - 38.67x slower

share|improve this answer

answered Feb 19 '16 at 23:07

pthammpthamm

1,5421814

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks for the benchmark. The accepted answer has the advantage of accepting inputs like 5.4e-29. I guess your regex could be tweaked to accept those also.
  
  – Jodi
  Feb 24 '16 at 16:27
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Handling cases like 1,000 is really hard, since it depends on user intention. There are many, many ways for humans to format numbers. Is 1,000 about equal to 1000, or about equal to 1? Most of the world says it's about 1, not a way to show the integer 1000.
  
  – James Moore
  Feb 25 '17 at 18:59
  

  
  
  
  

add a comment | 

5

Tl;dr: Use a regex approach. It is 39x faster than the rescue approach in the accepted answer and also handles cases like "1,000"

def regex_is_number? string

  no_commas =  string.gsub(',', '')

  matches = no_commas.match(/-?d+(?:.d+)?/)

  if !matches.nil? && matches.size == 1 && matches[0] == no_commas

    true

  else

    false

  end

end

--

The accepted answer by @Jakob S works for the most part, but catching exceptions can be really slow. In addition, the rescue approach fails on a string like "1,000".

Let's define the methods:

def rescue_is_number? string

  true if Float(string) rescue false

end



def regex_is_number? string

  no_commas =  string.gsub(',', '')

  matches = no_commas.match(/-?d+(?:.d+)?/)

  if !matches.nil? && matches.size == 1 && matches[0] == no_commas

    true

  else

    false

  end

end

And now some test cases:

test_cases = {

  true => ["5.5", "23", "-123", "1,234,123"],

  false => ["hello", "99designs", "(123)456-7890"]

}

And a little code to run the test cases:

test_cases.each do |expected_answer, cases|

  cases.each do |test_case|

    if rescue_is_number?(test_case) != expected_answer

      puts "**rescue_is_number? got #{test_case} wrong**"

    else

      puts "rescue_is_number? got #{test_case} right"

    end



    if regex_is_number?(test_case) != expected_answer

      puts "**regex_is_number? got #{test_case} wrong**"

    else

      puts "regex_is_number? got #{test_case} right"

    end  

  end

end

Here is the output of the test cases:

rescue_is_number? got 5.5 right

regex_is_number? got 5.5 right

rescue_is_number? got 23 right

regex_is_number? got 23 right

rescue_is_number? got -123 right

regex_is_number? got -123 right

**rescue_is_number? got 1,234,123 wrong**

regex_is_number? got 1,234,123 right

rescue_is_number? got hello right

regex_is_number? got hello right

rescue_is_number? got 99designs right

regex_is_number? got 99designs right

rescue_is_number? got (123)456-7890 right

regex_is_number? got (123)456-7890 right

Time to do some performance benchmarks:

Benchmark.ips do |x|



  x.report("rescue") { test_cases.values.flatten.each { |c| rescue_is_number? c } }

  x.report("regex") { test_cases.values.flatten.each { |c| regex_is_number? c } }



  x.compare!

end

And the results:

Calculating -------------------------------------

              rescue   128.000  i/100ms

               regex     4.649k i/100ms

-------------------------------------------------

              rescue      1.348k (±16.8%) i/s -      6.656k

               regex     52.113k (± 7.8%) i/s -    260.344k



Comparison:

               regex:    52113.3 i/s

              rescue:     1347.5 i/s - 38.67x slower

share|improve this answer

answered Feb 19 '16 at 23:07

pthammpthamm

1,5421814

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks for the benchmark. The accepted answer has the advantage of accepting inputs like 5.4e-29. I guess your regex could be tweaked to accept those also.
  
  – Jodi
  Feb 24 '16 at 16:27
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Handling cases like 1,000 is really hard, since it depends on user intention. There are many, many ways for humans to format numbers. Is 1,000 about equal to 1000, or about equal to 1? Most of the world says it's about 1, not a way to show the integer 1000.
  
  – James Moore
  Feb 25 '17 at 18:59
  

  
  
  
  

add a comment | 

5

5

5

Tl;dr: Use a regex approach. It is 39x faster than the rescue approach in the accepted answer and also handles cases like "1,000"

def regex_is_number? string

  no_commas =  string.gsub(',', '')

  matches = no_commas.match(/-?d+(?:.d+)?/)

  if !matches.nil? && matches.size == 1 && matches[0] == no_commas

    true

  else

    false

  end

end

--

The accepted answer by @Jakob S works for the most part, but catching exceptions can be really slow. In addition, the rescue approach fails on a string like "1,000".

Let's define the methods:

def rescue_is_number? string

  true if Float(string) rescue false

end



def regex_is_number? string

  no_commas =  string.gsub(',', '')

  matches = no_commas.match(/-?d+(?:.d+)?/)

  if !matches.nil? && matches.size == 1 && matches[0] == no_commas

    true

  else

    false

  end

end

And now some test cases:

test_cases = {

  true => ["5.5", "23", "-123", "1,234,123"],

  false => ["hello", "99designs", "(123)456-7890"]

}

And a little code to run the test cases:

test_cases.each do |expected_answer, cases|

  cases.each do |test_case|

    if rescue_is_number?(test_case) != expected_answer

      puts "**rescue_is_number? got #{test_case} wrong**"

    else

      puts "rescue_is_number? got #{test_case} right"

    end



    if regex_is_number?(test_case) != expected_answer

      puts "**regex_is_number? got #{test_case} wrong**"

    else

      puts "regex_is_number? got #{test_case} right"

    end  

  end

end

Here is the output of the test cases:

rescue_is_number? got 5.5 right

regex_is_number? got 5.5 right

rescue_is_number? got 23 right

regex_is_number? got 23 right

rescue_is_number? got -123 right

regex_is_number? got -123 right

**rescue_is_number? got 1,234,123 wrong**

regex_is_number? got 1,234,123 right

rescue_is_number? got hello right

regex_is_number? got hello right

rescue_is_number? got 99designs right

regex_is_number? got 99designs right

rescue_is_number? got (123)456-7890 right

regex_is_number? got (123)456-7890 right

Time to do some performance benchmarks:

Benchmark.ips do |x|



  x.report("rescue") { test_cases.values.flatten.each { |c| rescue_is_number? c } }

  x.report("regex") { test_cases.values.flatten.each { |c| regex_is_number? c } }



  x.compare!

end

And the results:

Calculating -------------------------------------

              rescue   128.000  i/100ms

               regex     4.649k i/100ms

-------------------------------------------------

              rescue      1.348k (±16.8%) i/s -      6.656k

               regex     52.113k (± 7.8%) i/s -    260.344k



Comparison:

               regex:    52113.3 i/s

              rescue:     1347.5 i/s - 38.67x slower

share|improve this answer

answered Feb 19 '16 at 23:07

pthammpthamm

1,5421814

Tl;dr: Use a regex approach. It is 39x faster than the rescue approach in the accepted answer and also handles cases like "1,000"

def regex_is_number? string

  no_commas =  string.gsub(',', '')

  matches = no_commas.match(/-?d+(?:.d+)?/)

  if !matches.nil? && matches.size == 1 && matches[0] == no_commas

    true

  else

    false

  end

end

--

The accepted answer by @Jakob S works for the most part, but catching exceptions can be really slow. In addition, the rescue approach fails on a string like "1,000".

Let's define the methods:

def rescue_is_number? string

  true if Float(string) rescue false

end



def regex_is_number? string

  no_commas =  string.gsub(',', '')

  matches = no_commas.match(/-?d+(?:.d+)?/)

  if !matches.nil? && matches.size == 1 && matches[0] == no_commas

    true

  else

    false

  end

end

And now some test cases:

test_cases = {

  true => ["5.5", "23", "-123", "1,234,123"],

  false => ["hello", "99designs", "(123)456-7890"]

}

And a little code to run the test cases:

test_cases.each do |expected_answer, cases|

  cases.each do |test_case|

    if rescue_is_number?(test_case) != expected_answer

      puts "**rescue_is_number? got #{test_case} wrong**"

    else

      puts "rescue_is_number? got #{test_case} right"

    end



    if regex_is_number?(test_case) != expected_answer

      puts "**regex_is_number? got #{test_case} wrong**"

    else

      puts "regex_is_number? got #{test_case} right"

    end  

  end

end

Here is the output of the test cases:

rescue_is_number? got 5.5 right

regex_is_number? got 5.5 right

rescue_is_number? got 23 right

regex_is_number? got 23 right

rescue_is_number? got -123 right

regex_is_number? got -123 right

**rescue_is_number? got 1,234,123 wrong**

regex_is_number? got 1,234,123 right

rescue_is_number? got hello right

regex_is_number? got hello right

rescue_is_number? got 99designs right

regex_is_number? got 99designs right

rescue_is_number? got (123)456-7890 right

regex_is_number? got (123)456-7890 right

Time to do some performance benchmarks:

Benchmark.ips do |x|



  x.report("rescue") { test_cases.values.flatten.each { |c| rescue_is_number? c } }

  x.report("regex") { test_cases.values.flatten.each { |c| regex_is_number? c } }



  x.compare!

end

And the results:

Calculating -------------------------------------

              rescue   128.000  i/100ms

               regex     4.649k i/100ms

-------------------------------------------------

              rescue      1.348k (±16.8%) i/s -      6.656k

               regex     52.113k (± 7.8%) i/s -    260.344k



Comparison:

               regex:    52113.3 i/s

              rescue:     1347.5 i/s - 38.67x slower

share|improve this answer

answered Feb 19 '16 at 23:07

pthammpthamm

1,5421814

share|improve this answer

share|improve this answer

answered Feb 19 '16 at 23:07

pthammpthamm

1,5421814

answered Feb 19 '16 at 23:07

pthammpthamm

1,5421814

answered Feb 19 '16 at 23:07

pthammpthamm

1,5421814

1,5421814

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks for the benchmark. The accepted answer has the advantage of accepting inputs like 5.4e-29. I guess your regex could be tweaked to accept those also.
  
  – Jodi
  Feb 24 '16 at 16:27
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Handling cases like 1,000 is really hard, since it depends on user intention. There are many, many ways for humans to format numbers. Is 1,000 about equal to 1000, or about equal to 1? Most of the world says it's about 1, not a way to show the integer 1000.
  
  – James Moore
  Feb 25 '17 at 18:59
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks for the benchmark. The accepted answer has the advantage of accepting inputs like 5.4e-29. I guess your regex could be tweaked to accept those also.
  
  – Jodi
  Feb 24 '16 at 16:27
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Handling cases like 1,000 is really hard, since it depends on user intention. There are many, many ways for humans to format numbers. Is 1,000 about equal to 1000, or about equal to 1? Most of the world says it's about 1, not a way to show the integer 1000.
  
  – James Moore
  Feb 25 '17 at 18:59
  

  
  
  
  

Thanks for the benchmark. The accepted answer has the advantage of accepting inputs like 5.4e-29. I guess your regex could be tweaked to accept those also.

– Jodi
Feb 24 '16 at 16:27

Thanks for the benchmark. The accepted answer has the advantage of accepting inputs like 5.4e-29. I guess your regex could be tweaked to accept those also.

– Jodi
Feb 24 '16 at 16:27

1

1

Handling cases like 1,000 is really hard, since it depends on user intention. There are many, many ways for humans to format numbers. Is 1,000 about equal to 1000, or about equal to 1? Most of the world says it's about 1, not a way to show the integer 1000.

– James Moore
Feb 25 '17 at 18:59

Handling cases like 1,000 is really hard, since it depends on user intention. There are many, many ways for humans to format numbers. Is 1,000 about equal to 1000, or about equal to 1? Most of the world says it's about 1, not a way to show the integer 1000.

– James Moore
Feb 25 '17 at 18:59

add a comment | 

4

this is how i do it, but i think too there must be a better way

object.to_i.to_s == object || object.to_f.to_s == object

share|improve this answer

answered Apr 14 '11 at 9:58

antpawantpaw

10k84278

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  It does not recognize floating notation, e.g. 1.2e+35.
  
  – hipertracker
  Jul 25 '12 at 16:13
  

  
  
  
  

add a comment | 

4

this is how i do it, but i think too there must be a better way

object.to_i.to_s == object || object.to_f.to_s == object

share|improve this answer

answered Apr 14 '11 at 9:58

antpawantpaw

10k84278

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  It does not recognize floating notation, e.g. 1.2e+35.
  
  – hipertracker
  Jul 25 '12 at 16:13
  

  
  
  
  

add a comment | 

4

4

4

this is how i do it, but i think too there must be a better way

object.to_i.to_s == object || object.to_f.to_s == object

share|improve this answer

answered Apr 14 '11 at 9:58

antpawantpaw

10k84278

this is how i do it, but i think too there must be a better way

object.to_i.to_s == object || object.to_f.to_s == object

share|improve this answer

answered Apr 14 '11 at 9:58

antpawantpaw

10k84278

share|improve this answer

share|improve this answer

answered Apr 14 '11 at 9:58

antpawantpaw

10k84278

answered Apr 14 '11 at 9:58

antpawantpaw

10k84278

answered Apr 14 '11 at 9:58

antpawantpaw

10k84278

10k84278

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  It does not recognize floating notation, e.g. 1.2e+35.
  
  – hipertracker
  Jul 25 '12 at 16:13
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  It does not recognize floating notation, e.g. 1.2e+35.
  
  – hipertracker
  Jul 25 '12 at 16:13
  

  
  
  
  

4

4

It does not recognize floating notation, e.g. 1.2e+35.

– hipertracker
Jul 25 '12 at 16:13

It does not recognize floating notation, e.g. 1.2e+35.

– hipertracker
Jul 25 '12 at 16:13

add a comment | 

4

In rails 4, you need to put
require File.expand_path('../../lib', __FILE__) + '/ext/string'
in your config/application.rb

share|improve this answer

answered May 19 '14 at 4:57

jcyejcye

515

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  actually you don't need to do this, you could just put string.rb in "initializers" and it works!
  
  – mahatmanich
  Jun 16 '14 at 8:32
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That's it! so cool!
  
  – zx1986
  Jul 7 '17 at 6:14
  

  
  
  
  

add a comment | 

4

In rails 4, you need to put
require File.expand_path('../../lib', __FILE__) + '/ext/string'
in your config/application.rb

share|improve this answer

answered May 19 '14 at 4:57

jcyejcye

515

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  actually you don't need to do this, you could just put string.rb in "initializers" and it works!
  
  – mahatmanich
  Jun 16 '14 at 8:32
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That's it! so cool!
  
  – zx1986
  Jul 7 '17 at 6:14
  

  
  
  
  

add a comment | 

4

4

4

In rails 4, you need to put
require File.expand_path('../../lib', __FILE__) + '/ext/string'
in your config/application.rb

share|improve this answer

answered May 19 '14 at 4:57

jcyejcye

515

In rails 4, you need to put
require File.expand_path('../../lib', __FILE__) + '/ext/string'
in your config/application.rb

share|improve this answer

answered May 19 '14 at 4:57

jcyejcye

515

share|improve this answer

share|improve this answer

answered May 19 '14 at 4:57

jcyejcye

515

answered May 19 '14 at 4:57

jcyejcye

515

answered May 19 '14 at 4:57

jcyejcye

515

515

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  actually you don't need to do this, you could just put string.rb in "initializers" and it works!
  
  – mahatmanich
  Jun 16 '14 at 8:32
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That's it! so cool!
  
  – zx1986
  Jul 7 '17 at 6:14
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  actually you don't need to do this, you could just put string.rb in "initializers" and it works!
  
  – mahatmanich
  Jun 16 '14 at 8:32
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That's it! so cool!
  
  – zx1986
  Jul 7 '17 at 6:14
  

  
  
  
  

1

1

actually you don't need to do this, you could just put string.rb in "initializers" and it works!

– mahatmanich
Jun 16 '14 at 8:32

actually you don't need to do this, you could just put string.rb in "initializers" and it works!

– mahatmanich
Jun 16 '14 at 8:32

That's it! so cool!

– zx1986
Jul 7 '17 at 6:14

That's it! so cool!

– zx1986
Jul 7 '17 at 6:14

add a comment | 

3

If you prefer not to use exceptions as part of the logic, you might try this:

class String

   def numeric?

    !!(self =~ /^-?d+(.d*)?$/)

  end

end

Or, if you want it to work across all object classes, replace class String with class Object an convert self to a string: !!(self.to_s =~ /^-?d+(.d*)?$/)

share|improve this answer

edited Apr 13 '17 at 2:50

answered Jun 7 '13 at 4:20

Mark SchneiderMark Schneider

13519

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Whats the purpose of negate and do nil? zero is trurthy on ruby, so you can do just !!(self =~ /^-?d+(.d*)?$/)
  
  – Arnold Roa
  Apr 11 '17 at 14:37
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Using !! certainly works. At least one Ruby style guide (github.com/bbatsov/ruby-style-guide) suggested avoiding !! in favor of .nil? for readability, but I've seen !! used in popular repositories, and I think it is a fine way to convert to boolean. I've edited the answer.
  
  – Mark Schneider
  Apr 13 '17 at 2:52
  

  
  
  
  

add a comment | 

3

If you prefer not to use exceptions as part of the logic, you might try this:

class String

   def numeric?

    !!(self =~ /^-?d+(.d*)?$/)

  end

end

Or, if you want it to work across all object classes, replace class String with class Object an convert self to a string: !!(self.to_s =~ /^-?d+(.d*)?$/)

share|improve this answer

edited Apr 13 '17 at 2:50

answered Jun 7 '13 at 4:20

Mark SchneiderMark Schneider

13519

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Whats the purpose of negate and do nil? zero is trurthy on ruby, so you can do just !!(self =~ /^-?d+(.d*)?$/)
  
  – Arnold Roa
  Apr 11 '17 at 14:37
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Using !! certainly works. At least one Ruby style guide (github.com/bbatsov/ruby-style-guide) suggested avoiding !! in favor of .nil? for readability, but I've seen !! used in popular repositories, and I think it is a fine way to convert to boolean. I've edited the answer.
  
  – Mark Schneider
  Apr 13 '17 at 2:52
  

  
  
  
  

add a comment | 

3

3

3

If you prefer not to use exceptions as part of the logic, you might try this:

class String

   def numeric?

    !!(self =~ /^-?d+(.d*)?$/)

  end

end

Or, if you want it to work across all object classes, replace class String with class Object an convert self to a string: !!(self.to_s =~ /^-?d+(.d*)?$/)

share|improve this answer

edited Apr 13 '17 at 2:50

answered Jun 7 '13 at 4:20

Mark SchneiderMark Schneider

13519

If you prefer not to use exceptions as part of the logic, you might try this:

class String

   def numeric?

    !!(self =~ /^-?d+(.d*)?$/)

  end

end

Or, if you want it to work across all object classes, replace class String with class Object an convert self to a string: !!(self.to_s =~ /^-?d+(.d*)?$/)

share|improve this answer

edited Apr 13 '17 at 2:50

answered Jun 7 '13 at 4:20

Mark SchneiderMark Schneider

13519

share|improve this answer

share|improve this answer

edited Apr 13 '17 at 2:50

edited Apr 13 '17 at 2:50

edited Apr 13 '17 at 2:50

answered Jun 7 '13 at 4:20

Mark SchneiderMark Schneider

13519

answered Jun 7 '13 at 4:20

Mark SchneiderMark Schneider

13519

answered Jun 7 '13 at 4:20

Mark SchneiderMark Schneider

13519

13519

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Whats the purpose of negate and do nil? zero is trurthy on ruby, so you can do just !!(self =~ /^-?d+(.d*)?$/)
  
  – Arnold Roa
  Apr 11 '17 at 14:37
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Using !! certainly works. At least one Ruby style guide (github.com/bbatsov/ruby-style-guide) suggested avoiding !! in favor of .nil? for readability, but I've seen !! used in popular repositories, and I think it is a fine way to convert to boolean. I've edited the answer.
  
  – Mark Schneider
  Apr 13 '17 at 2:52
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Whats the purpose of negate and do nil? zero is trurthy on ruby, so you can do just !!(self =~ /^-?d+(.d*)?$/)
  
  – Arnold Roa
  Apr 11 '17 at 14:37
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Using !! certainly works. At least one Ruby style guide (github.com/bbatsov/ruby-style-guide) suggested avoiding !! in favor of .nil? for readability, but I've seen !! used in popular repositories, and I think it is a fine way to convert to boolean. I've edited the answer.
  
  – Mark Schneider
  Apr 13 '17 at 2:52
  

  
  
  
  

Whats the purpose of negate and do nil? zero is trurthy on ruby, so you can do just !!(self =~ /^-?d+(.d*)?$/)

– Arnold Roa
Apr 11 '17 at 14:37

Whats the purpose of negate and do nil? zero is trurthy on ruby, so you can do just !!(self =~ /^-?d+(.d*)?$/)

– Arnold Roa
Apr 11 '17 at 14:37

Using !! certainly works. At least one Ruby style guide (github.com/bbatsov/ruby-style-guide) suggested avoiding !! in favor of .nil? for readability, but I've seen !! used in popular repositories, and I think it is a fine way to convert to boolean. I've edited the answer.

– Mark Schneider
Apr 13 '17 at 2:52

Using !! certainly works. At least one Ruby style guide (github.com/bbatsov/ruby-style-guide) suggested avoiding !! in favor of .nil? for readability, but I've seen !! used in popular repositories, and I think it is a fine way to convert to boolean. I've edited the answer.

– Mark Schneider
Apr 13 '17 at 2:52

add a comment | 

0

As of Ruby 2.6.0, the numeric cast-methods have an optional exception-argument [1]. This enables us to use the built-in methods without using exceptions as control flow:

Float('x') # => ArgumentError (invalid value for Float(): "x")

Float('x', exception: false) # => nil

Therefore, you don't have to define your own method, but can directly check variables like e.g.

if Float(my_var, exception: false)

  # do something if my_var is a float

end

share|improve this answer

answered Jan 3 at 12:59

TimitryTimitry

431614

add a comment | 

0

As of Ruby 2.6.0, the numeric cast-methods have an optional exception-argument [1]. This enables us to use the built-in methods without using exceptions as control flow:

Float('x') # => ArgumentError (invalid value for Float(): "x")

Float('x', exception: false) # => nil

Therefore, you don't have to define your own method, but can directly check variables like e.g.

if Float(my_var, exception: false)

  # do something if my_var is a float

end

share|improve this answer

answered Jan 3 at 12:59

TimitryTimitry

431614

add a comment | 

0

0

0

As of Ruby 2.6.0, the numeric cast-methods have an optional exception-argument [1]. This enables us to use the built-in methods without using exceptions as control flow:

Float('x') # => ArgumentError (invalid value for Float(): "x")

Float('x', exception: false) # => nil

Therefore, you don't have to define your own method, but can directly check variables like e.g.

if Float(my_var, exception: false)

  # do something if my_var is a float

end

share|improve this answer

answered Jan 3 at 12:59

TimitryTimitry

431614

As of Ruby 2.6.0, the numeric cast-methods have an optional exception-argument [1]. This enables us to use the built-in methods without using exceptions as control flow:

Float('x') # => ArgumentError (invalid value for Float(): "x")

Float('x', exception: false) # => nil

Therefore, you don't have to define your own method, but can directly check variables like e.g.

if Float(my_var, exception: false)

  # do something if my_var is a float

end

share|improve this answer

answered Jan 3 at 12:59

TimitryTimitry

431614

share|improve this answer

share|improve this answer

answered Jan 3 at 12:59

TimitryTimitry

431614

answered Jan 3 at 12:59

TimitryTimitry

431614

answered Jan 3 at 12:59

TimitryTimitry

431614

431614

add a comment | 

add a comment | 

-2

use the following function:

def is_numeric? val

    return val.try(:to_f).try(:to_s) == val

end

so,

is_numeric? "1.2f" = false

is_numeric? "1.2" = true

is_numeric? "12f" = false

is_numeric? "12" = true

share|improve this answer

answered Dec 22 '14 at 12:19

Rajesh PaulRajesh Paul

3,88562743

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This will fail if val is "0". Also note that the method .try isn't part of the Ruby core library and is only available if you're including ActiveSupport.
  
  – GMA
  Sep 17 '15 at 12:51
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In fact, it also fails for "12", so your fourth example in this question is wrong. "12.10" and "12.00" fail too.
  
  – GMA
  Sep 17 '15 at 12:52
  

  
  
  
  

add a comment | 

-2

use the following function:

def is_numeric? val

    return val.try(:to_f).try(:to_s) == val

end

so,

is_numeric? "1.2f" = false

is_numeric? "1.2" = true

is_numeric? "12f" = false

is_numeric? "12" = true

share|improve this answer

answered Dec 22 '14 at 12:19

Rajesh PaulRajesh Paul

3,88562743

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This will fail if val is "0". Also note that the method .try isn't part of the Ruby core library and is only available if you're including ActiveSupport.
  
  – GMA
  Sep 17 '15 at 12:51
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In fact, it also fails for "12", so your fourth example in this question is wrong. "12.10" and "12.00" fail too.
  
  – GMA
  Sep 17 '15 at 12:52
  

  
  
  
  

add a comment | 

-2

-2

-2

use the following function:

def is_numeric? val

    return val.try(:to_f).try(:to_s) == val

end

so,

is_numeric? "1.2f" = false

is_numeric? "1.2" = true

is_numeric? "12f" = false

is_numeric? "12" = true

share|improve this answer

answered Dec 22 '14 at 12:19

Rajesh PaulRajesh Paul

3,88562743

use the following function:

def is_numeric? val

    return val.try(:to_f).try(:to_s) == val

end

so,

is_numeric? "1.2f" = false

is_numeric? "1.2" = true

is_numeric? "12f" = false

is_numeric? "12" = true

share|improve this answer

answered Dec 22 '14 at 12:19

Rajesh PaulRajesh Paul

3,88562743

share|improve this answer

share|improve this answer

answered Dec 22 '14 at 12:19

Rajesh PaulRajesh Paul

3,88562743

answered Dec 22 '14 at 12:19

Rajesh PaulRajesh Paul

3,88562743

answered Dec 22 '14 at 12:19

Rajesh PaulRajesh Paul

3,88562743

3,88562743

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This will fail if val is "0". Also note that the method .try isn't part of the Ruby core library and is only available if you're including ActiveSupport.
  
  – GMA
  Sep 17 '15 at 12:51
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In fact, it also fails for "12", so your fourth example in this question is wrong. "12.10" and "12.00" fail too.
  
  – GMA
  Sep 17 '15 at 12:52
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This will fail if val is "0". Also note that the method .try isn't part of the Ruby core library and is only available if you're including ActiveSupport.
  
  – GMA
  Sep 17 '15 at 12:51
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In fact, it also fails for "12", so your fourth example in this question is wrong. "12.10" and "12.00" fail too.
  
  – GMA
  Sep 17 '15 at 12:52
  

  
  
  
  

This will fail if val is "0". Also note that the method .try isn't part of the Ruby core library and is only available if you're including ActiveSupport.

– GMA
Sep 17 '15 at 12:51

This will fail if val is "0". Also note that the method .try isn't part of the Ruby core library and is only available if you're including ActiveSupport.

– GMA
Sep 17 '15 at 12:51

In fact, it also fails for "12", so your fourth example in this question is wrong. "12.10" and "12.00" fail too.

– GMA
Sep 17 '15 at 12:52

In fact, it also fails for "12", so your fourth example in this question is wrong. "12.10" and "12.00" fail too.

– GMA
Sep 17 '15 at 12:52

add a comment | 

-5

How dumb is this solution?

def is_number?(i)

  begin

    i+0 == i

  rescue TypeError

    false

  end

end

share|improve this answer

answered Oct 6 '13 at 12:16

donvnielsendonvnielsen

837

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  This is sub-optimal because using '.respond_to?(:+)' is always better then failing and catching an exception on a specific method (:+) call. This might also fail for a variety of reasons were the Regex and conversion methods don't.
  
  – Sqeaky
  Apr 28 '14 at 17:17
  

  
  
  
  

add a comment | 

-5

How dumb is this solution?

def is_number?(i)

  begin

    i+0 == i

  rescue TypeError

    false

  end

end

share|improve this answer

answered Oct 6 '13 at 12:16

donvnielsendonvnielsen

837

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  This is sub-optimal because using '.respond_to?(:+)' is always better then failing and catching an exception on a specific method (:+) call. This might also fail for a variety of reasons were the Regex and conversion methods don't.
  
  – Sqeaky
  Apr 28 '14 at 17:17
  

  
  
  
  

add a comment | 

-5

-5

-5

How dumb is this solution?

def is_number?(i)

  begin

    i+0 == i

  rescue TypeError

    false

  end

end

share|improve this answer

answered Oct 6 '13 at 12:16

donvnielsendonvnielsen

837

How dumb is this solution?

def is_number?(i)

  begin

    i+0 == i

  rescue TypeError

    false

  end

end

share|improve this answer

answered Oct 6 '13 at 12:16

donvnielsendonvnielsen

837

share|improve this answer

share|improve this answer

answered Oct 6 '13 at 12:16

donvnielsendonvnielsen

837

answered Oct 6 '13 at 12:16

donvnielsendonvnielsen

837

answered Oct 6 '13 at 12:16

donvnielsendonvnielsen

837

837

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  This is sub-optimal because using '.respond_to?(:+)' is always better then failing and catching an exception on a specific method (:+) call. This might also fail for a variety of reasons were the Regex and conversion methods don't.
  
  – Sqeaky
  Apr 28 '14 at 17:17
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  This is sub-optimal because using '.respond_to?(:+)' is always better then failing and catching an exception on a specific method (:+) call. This might also fail for a variety of reasons were the Regex and conversion methods don't.
  
  – Sqeaky
  Apr 28 '14 at 17:17
  

  
  
  
  

1

1

This is sub-optimal because using '.respond_to?(:+)' is always better then failing and catching an exception on a specific method (:+) call. This might also fail for a variety of reasons were the Regex and conversion methods don't.

– Sqeaky
Apr 28 '14 at 17:17

This is sub-optimal because using '.respond_to?(:+)' is always better then failing and catching an exception on a specific method (:+) call. This might also fail for a variety of reasons were the Regex and conversion methods don't.

– Sqeaky
Apr 28 '14 at 17:17

add a comment | 

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