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

Den Delimarsky|Last Updated: 8/18/2017
1 Contributor

Builds a new array whose elements are the results of applying the given function to each of the elements of the array. The integer index passed to the function indicates the index of element being transformed.

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

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


// Signature:
Array.mapi : (int -> 'T -> 'U) -> 'T [] -> 'U []

// Usage:
Array.mapi mapping array


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

The function to transform elements and their indices.

array Type: 'T[]

The input array.

Return Value

The array of transformed elements.


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


The following code demonstrates the use of Array.mapi.

let array1 = [| 1; 2; 3 |]
let newArray = Array.mapi (fun i x -> (i, x)) array1
printfn "%A" newArray


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


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

Collections.Array Module (F#)

Microsoft.FSharp.Collections Namespace (F#)

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