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Map.tryFindKey<'Key,'T> Function (F#)

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

Returns the key of the first mapping in the collection that satisfies the given predicate, or returns None if no such element exists.

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

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


// Signature:
Map.tryFindKey : ('Key -> 'T -> bool) -> Map<'Key,'T> -> 'Key option (requires comparison)

// Usage:
Map.tryFindKey predicate table


predicate Type: 'Key -> 'T ->bool

The function to test the input elements.

table Type: Map<'Key,'T>

The input map.

Return Value

The first key for which the predicate returns true or None if the predicate evaluates to false for each key/value pair.


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


let map1 = [ for i in 1 .. 100 -> (i, i*i) ] |> Map.ofList
let result = Map.tryFindKey (fun key value -> key = value) map1
match result with
| Some key -> printfn "Found element with key %d." key
| None -> printfn "Did not find any element that matches the condition."


Found element with key 1.


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.Map Module (F#)

Microsoft.FSharp.Collections Namespace (F#)

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