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List.iteri2<'T1,'T2> Function (F#)

Applies the given function to two collections simultaneously. The collections must have identical size. The integer passed to the function indicates the index of element.

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

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

// Signature:
List.iteri2 : (int -> 'T1 -> 'T2 -> unit) -> 'T1 list -> 'T2 list -> unit

// Usage:
List.iteri2 action list1 list2

action

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

The function to apply to a pair of elements from the input lists along with their index.

list1

Type: 'T1 list

The first input list.

list2

Type: 'T2 list

The second input list.

Exception

Condition

ArgumentException

Thrown when the input lists differ in length.

This function is named IterateIndexed2 in compiled assemblies. If you are accessing the function from a language other than F#, or through reflection, use this name.

The following code example illustrates the use of List.iteri2 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

Windows 8, Windows 7, Windows Server 2012, Windows Server 2008 R2

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

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