Option.count<'T> Function (F#)

Article
2013-02-04

Evaluates the equivalent of Set.count for an option.

Namespace/Module Path: Microsoft.FSharp.Core.Option

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

// Signature:
count : 'T option -> int

// Usage:
count option

Parameters

option
Type: 'T option

The input option.

Return Value

A zero if the option is None, a one otherwise.

Remarks

The expression count inp evaluates to match inp with None -> 0 | Some _ -> 1.

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

Example

The following code illustrates the use of Option.count.

let opt1 = Some("test")
let opt2 = None
printfn "%A %A" (Option.count opt1) (Option.count opt2)

// Use Option.count to count the number of Some values in
// an array of options.
let getCount (array1 : int option array) =
    Array.fold (fun state elem -> state + Option.count elem) 0 array1
let testArray1 = [| Some(10); None; Some(1); None; None; Some(56) |]
let testArray2 = [| for i in 1 .. 10 do if i % 2 = 0 then yield Some(i) else yield None |]
printfn "%d" <| getCount testArray1
printfn "%d" <| getCount testArray2

Output

1 0
3
5

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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