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

Applies the given function f to each element x of the list. Returns the list comprised of the results for each element where the function returns Some(f(x)).

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

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

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

// Usage:
List.choose chooser list


  • chooser
    Type: 'T -> 'U option

    The function to generate options from the elements.

  • list
    Type: 'T list

    The input list.

Return Value

The list comprising the values selected from the chooser function.


This function is named Choose 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 List.choose to select capitalized words out of a list of words.

let listWords = [ "and"; "Rome"; "Bob"; "apple"; "zebra" ]
let isCapitalized (string1:string) = System.Char.IsUpper string1.[0]
let results = List.choose (fun elem ->
    match elem with
    | elem when isCapitalized elem -> Some(elem + "'s")
    | _ -> None) listWords
printfn "%A" results


["Rome's"; "Bob's"]


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


Supported in: 3

See Also


Collections.List Module (F#)

Microsoft.FSharp.Collections Namespace (F#)