List.mapi<'T,'U> Function (F#)

Article
04/28/2015

Creates a new collection whose elements are the results of applying the given function to each of the elements of the collection. The integer index passed to the function indicates the index (from 0) of element being transformed.

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

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

// Signature:
List.mapi : (int -> 'T -> 'U) -> 'T list -> 'U list

// Usage:
List.mapi mapping list

Parameters

mapping
Type: int -> 'T -> 'U

The function to transform elements and their indices.
list
Type: 'T list

The input list.

Return Value

The list of transformed elements.

Remarks

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

Example

The following code example illustrates the use of List.mapi.

let list1 = [1; 2; 3]
let newList = List.mapi (fun i x -> (i, x)) list1
printfn "%A" newList

Output

[(0, 1); (1, 2); (2, 3)]

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

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