Table of contents
Table of contents +
Visual F#
Visual F# Development Portal
What's new in Visual F#
Visual F# Guided Tour
Using Visual Studio to Write F# Programs
F# Language Reference
F# Compiler (fsc.exe) Reference
F# Interactive (fsi.exe) Reference
F# Core Library Reference
Microsoft.FSharp.Collections Namespace
Array Module
Array2D Module
Array3D Module
Array4D Module
ComparisonIdentity Module
HashIdentity Module
List Module
list<'T> Type Abbreviation
List<'T> Union
Map<'Key,'Value> Class
Collections.Map Module
Map.add<'Key,'T> Function
Map.containsKey<'Key,'T> Function
Map.empty<'Key,'T> Type Function
Map.exists<'Key,'T> Function
Map.filter<'Key,'T> Function
Map.find<'Key,'T> Function
Map.findKey<'Key,'T> Function
Map.fold<'Key,'T,'State> Function
Map.foldBack<'Key,'T,'State> Function
Map.forall<'Key,'T> Function
Map.isEmpty<'Key,'T> Function
Map.iter<'Key,'T> Function
Map.map<'Key,'T,'U> Function
Map.ofArray<'Key,'T> Function
Map.ofList<'Key,'T> Function
Map.ofSeq<'Key,'T> Function
Map.partition<'Key,'T> Function
Map.pick<'Key,'T,'U> Function
Map.remove<'Key,'T> Function
Map.toArray<'Key,'T> Function
Map.toList<'Key,'T> Function
Map.toSeq<'Key,'T> Function
Map.tryFind<'Key,'T> Function
Map.tryFindKey<'Key,'T> Function
Map.tryPick<'Key,'T,'U> Function
Collections.ResizeArray<'T> Type Abbreviation
Collections.Seq Module
Collections.seq<'T> Type Abbreviation
Collections.Set<'T> Class
Collections.Set Module
Microsoft.FSharp.Control Namespace (F#)
Microsoft.FSharp.Core Namespace (F#)
Microsoft.FSharp.Core.CompilerServices Namespace (F#)
Microsoft.FSharp.Data Namespace
Microsoft.FSharp.Linq Namespace (F#)
Microsoft.FSharp.NativeInterop Namespace (F#)
Microsoft.FSharp.Quotations Namespace (F#)
Microsoft.FSharp.Reflection Namespace (F#)
System Namespace (F#)
System.Collections Namespace (F#)
System.Numerics Namespace (F#)
System.Threading Namespace (F#)
Visual F# Samples and Walkthroughs
Type Providers (F#)
TOC
Collapse the table of content
Expand the table of content

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

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

Creates a new map containing only the bindings for which the given predicate returns true.

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

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

Syntax

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

// Usage:
Map.filter predicate table

Parameters

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

The function to test the key/value pairs.

table Type: Map<'Key,'T>

The input map.

Return Value

The filtered map.

Remarks

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

Example


printfn "Even numbers and their squares."
let map1 = Map.ofList [for i in 1 .. 10 -> (i, i*i)]
           |> Map.filter (fun key _ -> key % 2 = 0)
           |> Map.iter (fun key value -> printf "(%d, %d) " key value)
printfn ""

Output

Even numbers and their squares.
(2, 4) (4, 16) (6, 36) (8, 64) (10, 100)

Platforms

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#)

© 2019 Microsoft