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

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

Looks up an element in the map. If no binding exists in the map, raises System.Collections.Generic.KeyNotFoundException.

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

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


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

// Usage:
Map.find key table


key Type: 'Key

The input key.

table Type: Map<'Key,'T>

The input map.


KeyNotFoundExceptionThrown when the key does not exist in the map.

Return Value

The value mapped to the given key.


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


The following examples shows how to use Map.filter.

let findAndPrint key map =
    printfn "With key %d, found value %A." key (Map.find key map)
let map1 = Map.ofList [ (1, "one"); (2, "two"); (3, "three") ]
let map2 = Map.ofList [ for i in 1 .. 10 -> (i, i*i) ]
    findAndPrint 1 map1
    findAndPrint 2 map1
    findAndPrint 3 map2
    findAndPrint 5 map2
    // The key is not in the map, so this throws an exception.
    findAndPrint 0 map2
     :? System.Collections.Generic.KeyNotFoundException as e -> printfn "%s" e.Message


With key 1, found value "one".
With key 2, found value "two".
With key 3, found value 9.
With key 5, found value 25.
The given key was not present in the dictionary.


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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