List.mapi2<'T1,'T2,'U> Function (F#)

Article
2013-02-04

Like List.mapi, but mapping corresponding elements from two lists of equal length.

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

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

// Signature:
List.mapi2 : (int -> 'T1 -> 'T2 -> 'U) -> 'T1 list -> 'T2 list -> 'U list

// Usage:
List.mapi2 mapping list1 list2

Parameters

mapping
Type: int -> 'T1 -> 'T2 -> 'U

The function to transform pairs of elements from the two lists and their index.
list1
Type: 'T1 list

The first input list.
list2
Type: 'T2 list

The second input list.

Return Value

The list of transformed elements.

Remarks

This function is named MapIndexed2 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.mapi2.

let list1 = [1; 2; 3]
let list2 = [4; 5; 6]
let listAddTimesIndex = List.mapi2 (fun i x y -> (x + y) * i) list1 list2
printfn "%A" listAddTimesIndex

Output

[0; 7; 18]

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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