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Visual Studio 2012
Visual F#
F# Core Library Reference
Microsoft.FSharp.Collections Namespace
List Module
List.append<'T> Function
List.average<^T> Function
List.averageBy<'T,^U> Function
List.choose<'T,'U> Function
List.collect<'T,'U> Function
List.concat<'T> Function
List.empty<'T> Type Function
List.exists<'T> Function
List.exists2<'T1,'T2> Function
List.filter<'T> Function
List.find<'T> Function
List.findIndex<'T> Function
List.fold<'T,'State> Function
List.fold2<'T1,'T2,'State> Function
List.foldBack<'T,'State> Function
List.foldBack2<'T1,'T2,'State> Function
List.forall<'T> Function
List.forall2<'T1,'T2> Function
List.head<'T> Function
List.init<'T> Function
List.isEmpty<'T> Function
List.iter<'T> Function
List.iter2<'T1,'T2> Function
List.iteri<'T> Function
List.iteri2<'T1,'T2> Function
List.length<'T> Function
List.map<'T,'U> Function
List.map2<'T1,'T2,'U> Function
List.map3<'T1,'T2,'T3,'U> Function
List.mapi<'T,'U> Function
List.mapi2<'T1,'T2,'U> Function
List.max<'T> Function
List.maxBy<'T,'U> Function
List.min<'T> Function
List.minBy<'T,'U> Function
List.nth<'T> Function
List.ofArray<'T> Function
List.ofSeq<'T> Function
List.partition<'T> Function
List.permute<'T> Function
List.pick<'T,'U> Function
List.reduce<'T> Function
List.reduceBack<'T> Function
List.replicate<'T> Function
List.rev<'T> Function
List.scan<'T,'State> Function
List.scanBack<'T,'State> Function
List.sort<'T> Function
List.sortBy<'T,'Key> Function
List.sortWith<'T> Function
List.sum<^T> Function
List.sumBy<'T,^U> Function
List.tail<'T> Function
List.toArray<'T> Function
List.toSeq<'T> Function
List.tryFind<'T> Function
List.tryFindIndex<'T> Function
List.tryPick<'T,'U> Function
List.unzip<'T1,'T2> Function
List.unzip3<'T1,'T2,'T3> Function
List.zip<'T1,'T2> Function
List.zip3<'T1,'T2,'T3> Function
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List.filter<'T> Function (F#)

Visual Studio 2012

Returns a new collection containing only the elements of the collection for which the given predicate returns true.

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

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

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// Signature:
List.filter : ('T -> bool) -> 'T list -> 'T list

// Usage:
List.filter predicate list
predicate

Type: 'T -> bool

The function to test the input elements.

list

Type: 'T list

The input list.

A list containing only the elements that satisfy the predicate.

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

The following example demonstrates the use of List.filter.

F#
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let evenOnlyList = List.filter (fun x -> x % 2 = 0) [1; 2; 3; 4; 5; 6]

The resulting list is [2; 4; 6].

The following example shows another typical use for List.filter.

F#
Copy 
let data = [("Cats",4);
            ("Dogs",5);
            ("Mice",3);
            ("Elephants",2)]
let res = data |> List.filter (fun (nm,x) -> nm.Length <= 4)
printfn "Animals with short names: %A" res

Animals with short names: [("Cats", 4); ("Dogs", 5); ("Mice", 3)]

Windows 8, Windows 7, Windows Server 2012, Windows Server 2008 R2

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

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