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

  • Article

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

Parameters

  • 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.

Exceptions

Exception

Condition

ArgumentException

Thrown when the input lists differ in length.

Remarks

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.

Example

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

Platforms

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

Version Information

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

See Also

Reference

Collections.List Module (F#)

Microsoft.FSharp.Collections Namespace (F#)