Mixing
Eloquent Javascript: The sum of an array
I want a sum function that takes an array of numbers and returns the sum of these numbers.
I wrote the following, but it always returns undefined:
function sum(array){
var sumVar;
for(i = 0; i <= array[array.length]; i++){
sumVar += array[i];
}
return sumVar;
}
console.log(sum([1,2,3]));
// → undefined
Could anyone help explain why this is happening? I'm not so much concerned with the solution as I am with what I'm doing wrong.
javascript arrays
edited Jan 12 '15 at 2:58
Oriol
155k33260359
asked Jan 12 '15 at 2:20
sshafer15
61
add a comment |
I want a sum function that takes an array of numbers and returns the sum of these numbers.
I wrote the following, but it always returns undefined:
function sum(array){
var sumVar;
for(i = 0; i <= array[array.length]; i++){
sumVar += array[i];
}
return sumVar;
}
console.log(sum([1,2,3]));
// → undefined
Could anyone help explain why this is happening? I'm not so much concerned with the solution as I am with what I'm doing wrong.
javascript arrays
edited Jan 12 '15 at 2:58
Oriol
155k33260359
asked Jan 12 '15 at 2:20
sshafer15
61
3
an eloquent solution for sum would take advantage ofArray.prototype.reduce.
– zzzzBov
Jan 12 '15 at 2:35
add a comment |
I want a sum function that takes an array of numbers and returns the sum of these numbers.
I wrote the following, but it always returns undefined:
function sum(array){
var sumVar;
for(i = 0; i <= array[array.length]; i++){
sumVar += array[i];
}
return sumVar;
}
console.log(sum([1,2,3]));
// → undefined
Could anyone help explain why this is happening? I'm not so much concerned with the solution as I am with what I'm doing wrong.
javascript arrays
edited Jan 12 '15 at 2:58
Oriol
155k33260359
asked Jan 12 '15 at 2:20
sshafer15
61
I want a sum function that takes an array of numbers and returns the sum of these numbers.
I wrote the following, but it always returns undefined:
function sum(array){
var sumVar;
for(i = 0; i <= array[array.length]; i++){
sumVar += array[i];
}
return sumVar;
}
console.log(sum([1,2,3]));
// → undefined
Could anyone help explain why this is happening? I'm not so much concerned with the solution as I am with what I'm doing wrong.
javascript arrays
javascript arrays
edited Jan 12 '15 at 2:58
Oriol
155k33260359
asked Jan 12 '15 at 2:20
sshafer15
61
edited Jan 12 '15 at 2:58
Oriol
155k33260359
asked Jan 12 '15 at 2:20
sshafer15
61
edited Jan 12 '15 at 2:58
Oriol
155k33260359
edited Jan 12 '15 at 2:58
Oriol
155k33260359
edited Jan 12 '15 at 2:58
Oriol
155k33260359
155k33260359
asked Jan 12 '15 at 2:20
sshafer15
61
asked Jan 12 '15 at 2:20
sshafer15
61
asked Jan 12 '15 at 2:20
sshafer15
61
61
3
an eloquent solution for sum would take advantage ofArray.prototype.reduce.
– zzzzBov
Jan 12 '15 at 2:35
add a comment |
3
an eloquent solution for sum would take advantage ofArray.prototype.reduce.
– zzzzBov
Jan 12 '15 at 2:35
3
3
an eloquent solution for sum would take advantage of
Array.prototype.reduce.– zzzzBov
Jan 12 '15 at 2:35
an eloquent solution for sum would take advantage of
Array.prototype.reduce.– zzzzBov
Jan 12 '15 at 2:35
add a comment |
4 Answers
4
active
oldest
votes
While there are multiple areas of your code which seems incorrect (as addressed by @meagar), the reason why you still get undefined after changing your loop iteration to stop at array.length is because you didn't initialize sumVar to 0.
function sum (array) {
var sumVar = 0;
for(var i = 0; i < array.length; i += 1) {
sumVar += array[i];
}
return sumVar;
}
sum( [1, 2] ); // results in 3
answered Jan 12 '15 at 2:33
wmock
2,92322652
Thanks, that fixed it. Why do I need to initialize sumVar to zero?
– sshafer15
Jan 12 '15 at 2:37
2
You need to initialize sumVar to 0 because initially it's value isundefined. When you try to add numbers toundefined, what you'll end up with is the valueNaN.
– wmock
Jan 12 '15 at 2:39
add a comment |
Your condition, i <= array[array.length], makes no sense.
You're looping while i is less than array[array.length], which is one-past the last element of the array. This will typically be undefined. i <= undefined is always false, and obviously isn't what you want.
If you want to iterate over each element of the array, i is the index and you need to loop from 0 to one less than array.length. Your condition should be i < array.length.
answered Jan 12 '15 at 2:22
meagar♦
177k29272288
When I try this I get Not a Number. Any ideas why?
– sshafer15
Jan 12 '15 at 2:28
2
Small nitpick: The end condition of the for loop should bei < array.lengthsince JavaScript uses zero-based array indexing.
– Platinum Azure
Jan 12 '15 at 2:29
add a comment |
As @zzzzBov hinted in a comment, there is a more eloquent solution than the imperative loop, a solution involving some functional techniques:
var add = function(a, b) {return a + b;};
var sum = function(nums) {return nums.reduce(add, 0);};
In a library like Ramda, where functions like reduce are curried and the list parameter comes last, this would be even easier (although redundant, since Ramda already includes sum):
var sum = R.reduce(add, 0);
edited May 23 '17 at 10:30
Community♦
11
answered Jan 12 '15 at 4:39
Scott Sauyet
19.7k22653
Any comment to go with the downvote?
– Scott Sauyet
Jan 12 '15 at 19:01
I have just found out about Ramda today! How long has it been around? 2 years? BTW Isn't your R.reduce() missing the array param? It is nice we can now do R.sum([1,2,3,4,5]) without writing your sum function. We can code JS like Python with Ramda.
– yoshi
Nov 9 '16 at 13:20
Ramda's about 3 years old. But the first public announcement was in May, 2014. Not having the array parameter is very much intentional. If you want to see a long contentious discussion about the reason for it, there's one at github.com/ramda/ramda/issues/452. I don't think of it much like Python. More like Haskell, LISP, ML, F#, OCaml and other FP languages.
– Scott Sauyet
Nov 11 '16 at 2:47
Oh ok you did it intentionally. Sorry.
– yoshi
Nov 15 '16 at 12:13
add a comment |
You can try this:
function sumOfArray(array) {
return eval(array.join('+'));
}
console.log(sumOfArray([4,4])); // result 4+4 = 8
edited Nov 19 '18 at 16:06
DaFois
1,90641418
answered Nov 19 '18 at 15:52
Rahi
14
add a comment |
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4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
While there are multiple areas of your code which seems incorrect (as addressed by @meagar), the reason why you still get undefined after changing your loop iteration to stop at array.length is because you didn't initialize sumVar to 0.
function sum (array) {
var sumVar = 0;
for(var i = 0; i < array.length; i += 1) {
sumVar += array[i];
}
return sumVar;
}
sum( [1, 2] ); // results in 3
answered Jan 12 '15 at 2:33
wmock
2,92322652
Thanks, that fixed it. Why do I need to initialize sumVar to zero?
– sshafer15
Jan 12 '15 at 2:37
2
You need to initialize sumVar to 0 because initially it's value isundefined. When you try to add numbers toundefined, what you'll end up with is the valueNaN.
– wmock
Jan 12 '15 at 2:39
add a comment |
While there are multiple areas of your code which seems incorrect (as addressed by @meagar), the reason why you still get undefined after changing your loop iteration to stop at array.length is because you didn't initialize sumVar to 0.
function sum (array) {
var sumVar = 0;
for(var i = 0; i < array.length; i += 1) {
sumVar += array[i];
}
return sumVar;
}
sum( [1, 2] ); // results in 3
answered Jan 12 '15 at 2:33
wmock
2,92322652
Thanks, that fixed it. Why do I need to initialize sumVar to zero?
– sshafer15
Jan 12 '15 at 2:37
2
You need to initialize sumVar to 0 because initially it's value isundefined. When you try to add numbers toundefined, what you'll end up with is the valueNaN.
– wmock
Jan 12 '15 at 2:39
add a comment |
While there are multiple areas of your code which seems incorrect (as addressed by @meagar), the reason why you still get undefined after changing your loop iteration to stop at array.length is because you didn't initialize sumVar to 0.
function sum (array) {
var sumVar = 0;
for(var i = 0; i < array.length; i += 1) {
sumVar += array[i];
}
return sumVar;
}
sum( [1, 2] ); // results in 3
answered Jan 12 '15 at 2:33
wmock
2,92322652
While there are multiple areas of your code which seems incorrect (as addressed by @meagar), the reason why you still get undefined after changing your loop iteration to stop at array.length is because you didn't initialize sumVar to 0.
function sum (array) {
var sumVar = 0;
for(var i = 0; i < array.length; i += 1) {
sumVar += array[i];
}
return sumVar;
}
sum( [1, 2] ); // results in 3
answered Jan 12 '15 at 2:33
wmock
2,92322652
answered Jan 12 '15 at 2:33
wmock
2,92322652
answered Jan 12 '15 at 2:33
wmock
2,92322652
answered Jan 12 '15 at 2:33
wmock
2,92322652
2,92322652
Thanks, that fixed it. Why do I need to initialize sumVar to zero?
– sshafer15
Jan 12 '15 at 2:37
2
You need to initialize sumVar to 0 because initially it's value isundefined. When you try to add numbers toundefined, what you'll end up with is the valueNaN.
– wmock
Jan 12 '15 at 2:39
add a comment |
Thanks, that fixed it. Why do I need to initialize sumVar to zero?
– sshafer15
Jan 12 '15 at 2:37
2
You need to initialize sumVar to 0 because initially it's value isundefined. When you try to add numbers toundefined, what you'll end up with is the valueNaN.
– wmock
Jan 12 '15 at 2:39
Thanks, that fixed it. Why do I need to initialize sumVar to zero?
– sshafer15
Jan 12 '15 at 2:37
Thanks, that fixed it. Why do I need to initialize sumVar to zero?
– sshafer15
Jan 12 '15 at 2:37
2
2
You need to initialize sumVar to 0 because initially it's value is
undefined. When you try to add numbers to undefined, what you'll end up with is the value NaN.– wmock
Jan 12 '15 at 2:39
You need to initialize sumVar to 0 because initially it's value is
undefined. When you try to add numbers to undefined, what you'll end up with is the value NaN.– wmock
Jan 12 '15 at 2:39
add a comment |
Your condition, i <= array[array.length], makes no sense.
You're looping while i is less than array[array.length], which is one-past the last element of the array. This will typically be undefined. i <= undefined is always false, and obviously isn't what you want.
If you want to iterate over each element of the array, i is the index and you need to loop from 0 to one less than array.length. Your condition should be i < array.length.
answered Jan 12 '15 at 2:22
meagar♦
177k29272288
When I try this I get Not a Number. Any ideas why?
– sshafer15
Jan 12 '15 at 2:28
2
Small nitpick: The end condition of the for loop should bei < array.lengthsince JavaScript uses zero-based array indexing.
– Platinum Azure
Jan 12 '15 at 2:29
add a comment |
Your condition, i <= array[array.length], makes no sense.
You're looping while i is less than array[array.length], which is one-past the last element of the array. This will typically be undefined. i <= undefined is always false, and obviously isn't what you want.
If you want to iterate over each element of the array, i is the index and you need to loop from 0 to one less than array.length. Your condition should be i < array.length.
answered Jan 12 '15 at 2:22
meagar♦
177k29272288
When I try this I get Not a Number. Any ideas why?
– sshafer15
Jan 12 '15 at 2:28
2
Small nitpick: The end condition of the for loop should bei < array.lengthsince JavaScript uses zero-based array indexing.
– Platinum Azure
Jan 12 '15 at 2:29
add a comment |
Your condition, i <= array[array.length], makes no sense.
You're looping while i is less than array[array.length], which is one-past the last element of the array. This will typically be undefined. i <= undefined is always false, and obviously isn't what you want.
If you want to iterate over each element of the array, i is the index and you need to loop from 0 to one less than array.length. Your condition should be i < array.length.
answered Jan 12 '15 at 2:22
meagar♦
177k29272288
Your condition, i <= array[array.length], makes no sense.
You're looping while i is less than array[array.length], which is one-past the last element of the array. This will typically be undefined. i <= undefined is always false, and obviously isn't what you want.
If you want to iterate over each element of the array, i is the index and you need to loop from 0 to one less than array.length. Your condition should be i < array.length.
answered Jan 12 '15 at 2:22
meagar♦
177k29272288
edited Jan 12 '15 at 2:33
answered Jan 12 '15 at 2:22
meagar♦
177k29272288
answered Jan 12 '15 at 2:22
meagar♦
177k29272288
answered Jan 12 '15 at 2:22
meagar♦
177k29272288
177k29272288
When I try this I get Not a Number. Any ideas why?
– sshafer15
Jan 12 '15 at 2:28
2
Small nitpick: The end condition of the for loop should bei < array.lengthsince JavaScript uses zero-based array indexing.
– Platinum Azure
Jan 12 '15 at 2:29
add a comment |
When I try this I get Not a Number. Any ideas why?
– sshafer15
Jan 12 '15 at 2:28
2
Small nitpick: The end condition of the for loop should bei < array.lengthsince JavaScript uses zero-based array indexing.
– Platinum Azure
Jan 12 '15 at 2:29
When I try this I get Not a Number. Any ideas why?
– sshafer15
Jan 12 '15 at 2:28
When I try this I get Not a Number. Any ideas why?
– sshafer15
Jan 12 '15 at 2:28
2
2
Small nitpick: The end condition of the for loop should be
i < array.length since JavaScript uses zero-based array indexing.– Platinum Azure
Jan 12 '15 at 2:29
Small nitpick: The end condition of the for loop should be
i < array.length since JavaScript uses zero-based array indexing.– Platinum Azure
Jan 12 '15 at 2:29
add a comment |
As @zzzzBov hinted in a comment, there is a more eloquent solution than the imperative loop, a solution involving some functional techniques:
var add = function(a, b) {return a + b;};
var sum = function(nums) {return nums.reduce(add, 0);};
In a library like Ramda, where functions like reduce are curried and the list parameter comes last, this would be even easier (although redundant, since Ramda already includes sum):
var sum = R.reduce(add, 0);
edited May 23 '17 at 10:30
Community♦
11
answered Jan 12 '15 at 4:39
Scott Sauyet
19.7k22653
Any comment to go with the downvote?
– Scott Sauyet
Jan 12 '15 at 19:01
I have just found out about Ramda today! How long has it been around? 2 years? BTW Isn't your R.reduce() missing the array param? It is nice we can now do R.sum([1,2,3,4,5]) without writing your sum function. We can code JS like Python with Ramda.
– yoshi
Nov 9 '16 at 13:20
Ramda's about 3 years old. But the first public announcement was in May, 2014. Not having the array parameter is very much intentional. If you want to see a long contentious discussion about the reason for it, there's one at github.com/ramda/ramda/issues/452. I don't think of it much like Python. More like Haskell, LISP, ML, F#, OCaml and other FP languages.
– Scott Sauyet
Nov 11 '16 at 2:47
Oh ok you did it intentionally. Sorry.
– yoshi
Nov 15 '16 at 12:13
add a comment |
As @zzzzBov hinted in a comment, there is a more eloquent solution than the imperative loop, a solution involving some functional techniques:
var add = function(a, b) {return a + b;};
var sum = function(nums) {return nums.reduce(add, 0);};
In a library like Ramda, where functions like reduce are curried and the list parameter comes last, this would be even easier (although redundant, since Ramda already includes sum):
var sum = R.reduce(add, 0);
edited May 23 '17 at 10:30
Community♦
11
answered Jan 12 '15 at 4:39
Scott Sauyet
19.7k22653
Any comment to go with the downvote?
– Scott Sauyet
Jan 12 '15 at 19:01
I have just found out about Ramda today! How long has it been around? 2 years? BTW Isn't your R.reduce() missing the array param? It is nice we can now do R.sum([1,2,3,4,5]) without writing your sum function. We can code JS like Python with Ramda.
– yoshi
Nov 9 '16 at 13:20
Ramda's about 3 years old. But the first public announcement was in May, 2014. Not having the array parameter is very much intentional. If you want to see a long contentious discussion about the reason for it, there's one at github.com/ramda/ramda/issues/452. I don't think of it much like Python. More like Haskell, LISP, ML, F#, OCaml and other FP languages.
– Scott Sauyet
Nov 11 '16 at 2:47
Oh ok you did it intentionally. Sorry.
– yoshi
Nov 15 '16 at 12:13
add a comment |
As @zzzzBov hinted in a comment, there is a more eloquent solution than the imperative loop, a solution involving some functional techniques:
var add = function(a, b) {return a + b;};
var sum = function(nums) {return nums.reduce(add, 0);};
In a library like Ramda, where functions like reduce are curried and the list parameter comes last, this would be even easier (although redundant, since Ramda already includes sum):
var sum = R.reduce(add, 0);
edited May 23 '17 at 10:30
Community♦
11
answered Jan 12 '15 at 4:39
Scott Sauyet
19.7k22653
As @zzzzBov hinted in a comment, there is a more eloquent solution than the imperative loop, a solution involving some functional techniques:
var add = function(a, b) {return a + b;};
var sum = function(nums) {return nums.reduce(add, 0);};
In a library like Ramda, where functions like reduce are curried and the list parameter comes last, this would be even easier (although redundant, since Ramda already includes sum):
var sum = R.reduce(add, 0);
edited May 23 '17 at 10:30
Community♦
11
answered Jan 12 '15 at 4:39
Scott Sauyet
19.7k22653
edited May 23 '17 at 10:30
Community♦
11
edited May 23 '17 at 10:30
Community♦
11
edited May 23 '17 at 10:30
Community♦
11
11
answered Jan 12 '15 at 4:39
Scott Sauyet
19.7k22653
answered Jan 12 '15 at 4:39
Scott Sauyet
19.7k22653
answered Jan 12 '15 at 4:39
Scott Sauyet
19.7k22653
19.7k22653
Any comment to go with the downvote?
– Scott Sauyet
Jan 12 '15 at 19:01
I have just found out about Ramda today! How long has it been around? 2 years? BTW Isn't your R.reduce() missing the array param? It is nice we can now do R.sum([1,2,3,4,5]) without writing your sum function. We can code JS like Python with Ramda.
– yoshi
Nov 9 '16 at 13:20
Ramda's about 3 years old. But the first public announcement was in May, 2014. Not having the array parameter is very much intentional. If you want to see a long contentious discussion about the reason for it, there's one at github.com/ramda/ramda/issues/452. I don't think of it much like Python. More like Haskell, LISP, ML, F#, OCaml and other FP languages.
– Scott Sauyet
Nov 11 '16 at 2:47
Oh ok you did it intentionally. Sorry.
– yoshi
Nov 15 '16 at 12:13
add a comment |
Any comment to go with the downvote?
– Scott Sauyet
Jan 12 '15 at 19:01
I have just found out about Ramda today! How long has it been around? 2 years? BTW Isn't your R.reduce() missing the array param? It is nice we can now do R.sum([1,2,3,4,5]) without writing your sum function. We can code JS like Python with Ramda.
– yoshi
Nov 9 '16 at 13:20
Ramda's about 3 years old. But the first public announcement was in May, 2014. Not having the array parameter is very much intentional. If you want to see a long contentious discussion about the reason for it, there's one at github.com/ramda/ramda/issues/452. I don't think of it much like Python. More like Haskell, LISP, ML, F#, OCaml and other FP languages.
– Scott Sauyet
Nov 11 '16 at 2:47
Oh ok you did it intentionally. Sorry.
– yoshi
Nov 15 '16 at 12:13
Any comment to go with the downvote?
– Scott Sauyet
Jan 12 '15 at 19:01
Any comment to go with the downvote?
– Scott Sauyet
Jan 12 '15 at 19:01
I have just found out about Ramda today! How long has it been around? 2 years? BTW Isn't your R.reduce() missing the array param? It is nice we can now do R.sum([1,2,3,4,5]) without writing your sum function. We can code JS like Python with Ramda.
– yoshi
Nov 9 '16 at 13:20
I have just found out about Ramda today! How long has it been around? 2 years? BTW Isn't your R.reduce() missing the array param? It is nice we can now do R.sum([1,2,3,4,5]) without writing your sum function. We can code JS like Python with Ramda.
– yoshi
Nov 9 '16 at 13:20
Ramda's about 3 years old. But the first public announcement was in May, 2014. Not having the array parameter is very much intentional. If you want to see a long contentious discussion about the reason for it, there's one at github.com/ramda/ramda/issues/452. I don't think of it much like Python. More like Haskell, LISP, ML, F#, OCaml and other FP languages.
– Scott Sauyet
Nov 11 '16 at 2:47
Ramda's about 3 years old. But the first public announcement was in May, 2014. Not having the array parameter is very much intentional. If you want to see a long contentious discussion about the reason for it, there's one at github.com/ramda/ramda/issues/452. I don't think of it much like Python. More like Haskell, LISP, ML, F#, OCaml and other FP languages.
– Scott Sauyet
Nov 11 '16 at 2:47
Oh ok you did it intentionally. Sorry.
– yoshi
Nov 15 '16 at 12:13
Oh ok you did it intentionally. Sorry.
– yoshi
Nov 15 '16 at 12:13
add a comment |
You can try this:
function sumOfArray(array) {
return eval(array.join('+'));
}
console.log(sumOfArray([4,4])); // result 4+4 = 8
edited Nov 19 '18 at 16:06
DaFois
1,90641418
answered Nov 19 '18 at 15:52
Rahi
14
add a comment |
You can try this:
function sumOfArray(array) {
return eval(array.join('+'));
}
console.log(sumOfArray([4,4])); // result 4+4 = 8
edited Nov 19 '18 at 16:06
DaFois
1,90641418
answered Nov 19 '18 at 15:52
Rahi
14
add a comment |
You can try this:
function sumOfArray(array) {
return eval(array.join('+'));
}
console.log(sumOfArray([4,4])); // result 4+4 = 8
edited Nov 19 '18 at 16:06
DaFois
1,90641418
answered Nov 19 '18 at 15:52
Rahi
14
You can try this:
function sumOfArray(array) {
return eval(array.join('+'));
}
console.log(sumOfArray([4,4])); // result 4+4 = 8
edited Nov 19 '18 at 16:06
DaFois
1,90641418
answered Nov 19 '18 at 15:52
Rahi
14
edited Nov 19 '18 at 16:06
DaFois
1,90641418
edited Nov 19 '18 at 16:06
DaFois
1,90641418
edited Nov 19 '18 at 16:06
DaFois
1,90641418
1,90641418
answered Nov 19 '18 at 15:52
Rahi
14
answered Nov 19 '18 at 15:52
Rahi
14
answered Nov 19 '18 at 15:52
Rahi
14
14
add a comment |
add a comment |
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an eloquent solution for sum would take advantage of
Array.prototype.reduce.– zzzzBov
Jan 12 '15 at 2:35