Mixing
Problem in converting from for-comprehension to map
I'm trying to convert a Scala for comprehension into using map and I'm running into a problem.
For illustration, consider that following conversion that works as expected.
scala> for (i <- 0 to 10) yield i * 2
res0: scala.collection.immutable.IndexedSeq[Int] = Vector(0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
scala> 0 to 10 map { _ * 2 }
res1: scala.collection.immutable.IndexedSeq[Int] = Vector(0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
However, the following isn't working. What mistake am I making?
scala> import util.Random
import util.Random
scala> for (i <- 0 to 10) yield Random.nextInt(10)
res2: scala.collection.immutable.IndexedSeq[Int] = Vector(3, 0, 7, 5, 9, 4, 6, 6, 6, 3, 0)
scala> 0 to 10 map { Random.nextInt(10) }
<console>:13: error: type mismatch;
found : Int
required: Int => ?
0 to 10 map { Random.nextInt(10) }
^
The root cause might be either my inability to correctly decipher the error message or fixing the cause. As I review the signature of Random.nextInt it seems to be returning an Int.
scala> Random.nextInt
def nextInt(n: Int): Int def nextInt(): Int
Error message is saying that I need to provide a function that takes an Int and returns "something" (not sure what ? stands for).
required: Int => ?
So I can see that there is a mismatch. But how do I convert what I want to happen -- a call to Random.nextInt(10) -- into a function and pass it to map?
Any help in understanding the error message below would be appreciated.
scala> 0 to 10 map { Random.nextInt(10) }
<console>:13: error: type mismatch;
found : Int
required: Int => ?
0 to 10 map { Random.nextInt(10) }
^
(Edit)
Doing the following helped.
scala> def foo(x: Int): Int = Random.nextInt(10)
foo: (x: Int)Int
scala> 0 to 10 map { foo }
res10: scala.collection.immutable.IndexedSeq[Int] = Vector(0, 2, 1, 7, 6, 5, 1, 6, 0, 7, 4)
But comments on this or suggestions of recommended Scala-way to do this would be appreciated.
scala for-comprehension
asked Jan 1 at 22:03
Alok LalAlok Lal
6018
add a comment |
I'm trying to convert a Scala for comprehension into using map and I'm running into a problem.
For illustration, consider that following conversion that works as expected.
scala> for (i <- 0 to 10) yield i * 2
res0: scala.collection.immutable.IndexedSeq[Int] = Vector(0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
scala> 0 to 10 map { _ * 2 }
res1: scala.collection.immutable.IndexedSeq[Int] = Vector(0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
However, the following isn't working. What mistake am I making?
scala> import util.Random
import util.Random
scala> for (i <- 0 to 10) yield Random.nextInt(10)
res2: scala.collection.immutable.IndexedSeq[Int] = Vector(3, 0, 7, 5, 9, 4, 6, 6, 6, 3, 0)
scala> 0 to 10 map { Random.nextInt(10) }
<console>:13: error: type mismatch;
found : Int
required: Int => ?
0 to 10 map { Random.nextInt(10) }
^
The root cause might be either my inability to correctly decipher the error message or fixing the cause. As I review the signature of Random.nextInt it seems to be returning an Int.
scala> Random.nextInt
def nextInt(n: Int): Int def nextInt(): Int
Error message is saying that I need to provide a function that takes an Int and returns "something" (not sure what ? stands for).
required: Int => ?
So I can see that there is a mismatch. But how do I convert what I want to happen -- a call to Random.nextInt(10) -- into a function and pass it to map?
Any help in understanding the error message below would be appreciated.
scala> 0 to 10 map { Random.nextInt(10) }
<console>:13: error: type mismatch;
found : Int
required: Int => ?
0 to 10 map { Random.nextInt(10) }
^
(Edit)
Doing the following helped.
scala> def foo(x: Int): Int = Random.nextInt(10)
foo: (x: Int)Int
scala> 0 to 10 map { foo }
res10: scala.collection.immutable.IndexedSeq[Int] = Vector(0, 2, 1, 7, 6, 5, 1, 6, 0, 7, 4)
But comments on this or suggestions of recommended Scala-way to do this would be appreciated.
scala for-comprehension
asked Jan 1 at 22:03
Alok LalAlok Lal
6018
add a comment |
I'm trying to convert a Scala for comprehension into using map and I'm running into a problem.
For illustration, consider that following conversion that works as expected.
scala> for (i <- 0 to 10) yield i * 2
res0: scala.collection.immutable.IndexedSeq[Int] = Vector(0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
scala> 0 to 10 map { _ * 2 }
res1: scala.collection.immutable.IndexedSeq[Int] = Vector(0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
However, the following isn't working. What mistake am I making?
scala> import util.Random
import util.Random
scala> for (i <- 0 to 10) yield Random.nextInt(10)
res2: scala.collection.immutable.IndexedSeq[Int] = Vector(3, 0, 7, 5, 9, 4, 6, 6, 6, 3, 0)
scala> 0 to 10 map { Random.nextInt(10) }
<console>:13: error: type mismatch;
found : Int
required: Int => ?
0 to 10 map { Random.nextInt(10) }
^
The root cause might be either my inability to correctly decipher the error message or fixing the cause. As I review the signature of Random.nextInt it seems to be returning an Int.
scala> Random.nextInt
def nextInt(n: Int): Int def nextInt(): Int
Error message is saying that I need to provide a function that takes an Int and returns "something" (not sure what ? stands for).
required: Int => ?
So I can see that there is a mismatch. But how do I convert what I want to happen -- a call to Random.nextInt(10) -- into a function and pass it to map?
Any help in understanding the error message below would be appreciated.
scala> 0 to 10 map { Random.nextInt(10) }
<console>:13: error: type mismatch;
found : Int
required: Int => ?
0 to 10 map { Random.nextInt(10) }
^
(Edit)
Doing the following helped.
scala> def foo(x: Int): Int = Random.nextInt(10)
foo: (x: Int)Int
scala> 0 to 10 map { foo }
res10: scala.collection.immutable.IndexedSeq[Int] = Vector(0, 2, 1, 7, 6, 5, 1, 6, 0, 7, 4)
But comments on this or suggestions of recommended Scala-way to do this would be appreciated.
scala for-comprehension
asked Jan 1 at 22:03
Alok LalAlok Lal
6018
I'm trying to convert a Scala for comprehension into using map and I'm running into a problem.
For illustration, consider that following conversion that works as expected.
scala> for (i <- 0 to 10) yield i * 2
res0: scala.collection.immutable.IndexedSeq[Int] = Vector(0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
scala> 0 to 10 map { _ * 2 }
res1: scala.collection.immutable.IndexedSeq[Int] = Vector(0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
However, the following isn't working. What mistake am I making?
scala> import util.Random
import util.Random
scala> for (i <- 0 to 10) yield Random.nextInt(10)
res2: scala.collection.immutable.IndexedSeq[Int] = Vector(3, 0, 7, 5, 9, 4, 6, 6, 6, 3, 0)
scala> 0 to 10 map { Random.nextInt(10) }
<console>:13: error: type mismatch;
found : Int
required: Int => ?
0 to 10 map { Random.nextInt(10) }
^
The root cause might be either my inability to correctly decipher the error message or fixing the cause. As I review the signature of Random.nextInt it seems to be returning an Int.
scala> Random.nextInt
def nextInt(n: Int): Int def nextInt(): Int
Error message is saying that I need to provide a function that takes an Int and returns "something" (not sure what ? stands for).
required: Int => ?
So I can see that there is a mismatch. But how do I convert what I want to happen -- a call to Random.nextInt(10) -- into a function and pass it to map?
Any help in understanding the error message below would be appreciated.
scala> 0 to 10 map { Random.nextInt(10) }
<console>:13: error: type mismatch;
found : Int
required: Int => ?
0 to 10 map { Random.nextInt(10) }
^
(Edit)
Doing the following helped.
scala> def foo(x: Int): Int = Random.nextInt(10)
foo: (x: Int)Int
scala> 0 to 10 map { foo }
res10: scala.collection.immutable.IndexedSeq[Int] = Vector(0, 2, 1, 7, 6, 5, 1, 6, 0, 7, 4)
But comments on this or suggestions of recommended Scala-way to do this would be appreciated.
scala for-comprehension
scala for-comprehension
asked Jan 1 at 22:03
Alok LalAlok Lal
6018
asked Jan 1 at 22:03
Alok LalAlok Lal
6018
edited Jan 1 at 22:09
Alok Lal
asked Jan 1 at 22:03
Alok LalAlok Lal
6018
asked Jan 1 at 22:03
Alok LalAlok Lal
6018
asked Jan 1 at 22:03
Alok LalAlok Lal
6018
6018
add a comment |
add a comment |
1 Answer
1
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oldest
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The Int => ? in the error message means than the compiler expects to see a function from Int to some other type (?). But Random.nextInt(10) is not a function, it's just an Int. You have to take an integer parameter:
0 to 10 map { i => Random.nextInt(10) }
You can also explicitly ignore the argument:
0 to 10 map { _ => Random.nextInt(10) }
or, even better, just use fill:
Vector.fill(10){ Random.nextInt(10) }
answered Jan 1 at 22:09
Andrey TyukinAndrey Tyukin
29.4k42351
add a comment |
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1 Answer
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1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
The Int => ? in the error message means than the compiler expects to see a function from Int to some other type (?). But Random.nextInt(10) is not a function, it's just an Int. You have to take an integer parameter:
0 to 10 map { i => Random.nextInt(10) }
You can also explicitly ignore the argument:
0 to 10 map { _ => Random.nextInt(10) }
or, even better, just use fill:
Vector.fill(10){ Random.nextInt(10) }
answered Jan 1 at 22:09
Andrey TyukinAndrey Tyukin
29.4k42351
add a comment |
The Int => ? in the error message means than the compiler expects to see a function from Int to some other type (?). But Random.nextInt(10) is not a function, it's just an Int. You have to take an integer parameter:
0 to 10 map { i => Random.nextInt(10) }
You can also explicitly ignore the argument:
0 to 10 map { _ => Random.nextInt(10) }
or, even better, just use fill:
Vector.fill(10){ Random.nextInt(10) }
answered Jan 1 at 22:09
Andrey TyukinAndrey Tyukin
29.4k42351
add a comment |
The Int => ? in the error message means than the compiler expects to see a function from Int to some other type (?). But Random.nextInt(10) is not a function, it's just an Int. You have to take an integer parameter:
0 to 10 map { i => Random.nextInt(10) }
You can also explicitly ignore the argument:
0 to 10 map { _ => Random.nextInt(10) }
or, even better, just use fill:
Vector.fill(10){ Random.nextInt(10) }
answered Jan 1 at 22:09
Andrey TyukinAndrey Tyukin
29.4k42351
The Int => ? in the error message means than the compiler expects to see a function from Int to some other type (?). But Random.nextInt(10) is not a function, it's just an Int. You have to take an integer parameter:
0 to 10 map { i => Random.nextInt(10) }
You can also explicitly ignore the argument:
0 to 10 map { _ => Random.nextInt(10) }
or, even better, just use fill:
Vector.fill(10){ Random.nextInt(10) }
answered Jan 1 at 22:09
Andrey TyukinAndrey Tyukin
29.4k42351
answered Jan 1 at 22:09
Andrey TyukinAndrey Tyukin
29.4k42351
answered Jan 1 at 22:09
Andrey TyukinAndrey Tyukin
29.4k42351
answered Jan 1 at 22:09
Andrey TyukinAndrey Tyukin
29.4k42351
29.4k42351
add a comment |
add a comment |
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