List.iter2<'T1,'T2> Function (F#)

Article
2013-02-04

Applies the given function to two collections simultaneously. The collections must have identical size.

Namespace/Module Path: Microsoft.FSharp.Collections.List

Assembly: FSharp.Core (in FSharp.Core.dll)

// Signature:
List.iter2 : ('T1 -> 'T2 -> unit) -> 'T1 list -> 'T2 list -> unit

// Usage:
List.iter2 action list1 list2

Parameters

action
Type: 'T1 -> 'T2 -> unit

The function to apply to pairs of elements from the input lists.
list1
Type: 'T1 list

The first input list.
list2
Type: 'T2 list

The second input list.

Exceptions

Exception	Condition
ArgumentException	Thrown when the input lists differ in length.

Remarks

This function is named Iterate2 in compiled assemblies. If you are accessing the function from a language other than F#, or through reflection, use this name.

Example

The following code example illustrates the use of List.iter2 and compares its behavior with related functions.

let list1 = [1; 2; 3]
let list2 = [4; 5; 6]
List.iter (fun x -> printfn "List.iter: element is %d" x) list1
List.iteri(fun i x -> printfn "List.iteri: element %d is %d" i x) list1
List.iter2 (fun x y -> printfn "List.iter2: elements are %d %d" x y) list1 list2
List.iteri2 (fun i x y ->
               printfn "List.iteri2: element %d of list1 is %d element %d of list2 is %d"
                 i x i y)
            list1 list2

Output

List.iter: element is 1
List.iter: element is 2
List.iter: element is 3
List.iteri: element 0 is 1
List.iteri: element 1 is 2
List.iteri: element 2 is 3
List.iter2: elements are 1 4
List.iter2: elements are 2 5
List.iter2: elements are 3 6
List.iteri2: element 0 of list1 is 1 element 0 of list2 is 4
List.iteri2: element 1 of list1 is 2 element 1 of list2 is 5
List.iteri2: element 2 of list1 is 3 element 2 of list2 is 6

Platforms

Windows 7, Windows Vista SP2, Windows XP SP3, Windows XP x64 SP2, Windows Server 2008 R2, Windows Server 2008 SP2, Windows Server 2003 SP2

Version Information

F# Runtime

Supported in: 2.0, 4.0

Silverlight

Supported in: 3

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