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Enumerable.Single<TSource> Method (IEnumerable<TSource>)

 

Returns the only element of a sequence, and throws an exception if there is not exactly one element in the sequence.

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

public static TSource Single<TSource>(
	this IEnumerable<TSource> source
)

Parameters

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

An IEnumerable<T> to return the single element of.

Return Value

Type: TSource

The single element of the input sequence.

Type Parameters

TSource

The type of the elements of source.

Exception Condition
ArgumentNullException

source is null.

InvalidOperationException

The input sequence contains more than one element.

-or-

The input sequence is empty.

The Single<TSource>(IEnumerable<TSource>) method throws an exception if the input sequence is empty. To instead return null when the input sequence is empty, use SingleOrDefault<TSource>.

The following code example demonstrates how to use Single<TSource>(IEnumerable<TSource>) to select the only element of an array.

string[] fruits1 = { "orange" };

string fruit1 = fruits1.Single();

Console.WriteLine(fruit1);

/*
 This code produces the following output:

 orange
*/

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

string[] fruits2 = { "orange", "apple" };
string fruit2 = null;

try
{
    fruit2 = fruits2.Single();
}
catch (System.InvalidOperationException)
{
    Console.WriteLine("The collection does not contain exactly one element.");
}

Console.WriteLine(fruit2);

/*
 This code produces the following output:

 The collection does not contain exactly one element.
*/

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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