Enumerable.Single<'TSource> Method (IEnumerable<'TSource>, Func<'TSource, Boolean>)

 

Returns the only element of a sequence that satisfies a specified condition, and throws an exception if more than one such element exists.

Namespace:   System.Linq
Assembly:  System.Core (in System.Core.dll)

static member Single<'TSource> : 
        source:IEnumerable<'TSource> *
        predicate:Func<'TSource, bool> -> 'TSource

Parameters

source
Type: System.Collections.Generic.IEnumerable<'TSource>

An IEnumerable<'T> to return a single element from.

predicate
Type: System.Func<'TSource, Boolean>

A function to test an element for a condition.

Return Value

Type: TSource

The single element of the input sequence that satisfies a condition.

Type Parameters

TSource

The type of the elements of source.

Exception Condition
ArgumentNullException

source or predicate is null.

InvalidOperationException

No element satisfies the condition in predicate.

-or-

More than one element satisfies the condition in predicate.

-or-

The source sequence is empty.

The Single<'TSource>(IEnumerable<'TSource>, Func<'TSource, Boolean>) method throws an exception if the input sequence contains no matching element. To instead return null when no matching element is found, use SingleOrDefault<'TSource>.

The following code example demonstrates how to use Single<'TSource>(IEnumerable<'TSource>, Func<'TSource, Boolean>) to select the only element of an array that satisfies a condition.

No code example is currently available or this language may not be supported.

The following code example demonstrates that Single<'TSource>(IEnumerable<'TSource>, Func<'TSource, Boolean>) throws an exception when the sequence does not contain exactly one element that satisfies the condition.

No code example is currently available or this language may not be supported.

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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