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

Статья
02/04/2013

Applies the given function to successive elements, returning the first result where function returns Some for some value. If no such element exists then this function raises KeyNotFoundException.

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

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

// Signature:
List.pick : ('T -> 'U option) -> 'T list -> 'U

// Usage:
List.pick chooser list

Parameters

chooser
Type: 'T -> 'U option

The function to generate options from the elements.
list
Type: 'T list

The input list.

Exceptions

Exception	Condition
KeyNotFoundException	Thrown when a matching element is not found or when the list is empty.

Return Value

The first resulting value where Some is returned.

Remarks

This function is named Pick 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.pick.

let valuesList = [ ("a", 1); ("b", 2); ("c", 3) ]

let resultPick = List.pick (fun elem ->
                    match elem with
                    | (value, 2) -> Some value
                    | _ -> None) valuesList
printfn "%A" resultPick

Output

"b"

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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