seq.mapi['t,'u]-function-[fsharp].md

title	Seq.mapi<'T,'U> Function (F#)
description	Seq.mapi<'T,'U> Function (F#)
keywords	visual f#, f#, functional programming
author	dend
manager	danielfe
ms.date	05/16/2016
ms.topic	language-reference
ms.prod	visual-studio-dev14
ms.technology	devlang-fsharp
ms.assetid	6609c9fd-fda3-40b0-b794-ff88b7796c92

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

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.Seq

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

Syntax

// Signature:
Seq.mapi : (int -> 'T -> 'U) -> seq<'T> -> seq<'U>

// Usage:
Seq.mapi mapping source

Parameters

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

A function to transform items from the input sequence that also supplies the current index.

source Type: seq<'T>

The input sequence.

Exceptions

Exception	Condition
ArgumentNullException	Thrown when the input sequence is null.

Return Value

The result sequence.

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

let text = "hello"
Seq.mapi (fun i c -> sprintf "%d - %c" i c) text |> Seq.iter (fun s -> printfn "%s" s)

Output

0 - h
1 - e
2 - l
3 - l
4 - o

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

Collections.Seq Module (F#)

Microsoft.FSharp.Collections Namespace (F#)