Export (0) Print
Expand All

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
Assemblies:   System.Linq (in System.Linq.dll)
  System.Core (in System.Core.dll)

public static TSource Single<TSource>(
	this IEnumerable<TSource> source,
	Func<TSource, bool> predicate
)

Type Parameters

TSource

The type of the elements of source.

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.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable<TSource>. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

ExceptionCondition
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.

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.

            string[] fruits = { "apple", "banana", "mango", 
                                  "orange", "passionfruit", "grape" };

            string fruit1 = fruits.Single(fruit => fruit.Length > 10);

            Console.WriteLine(fruit1);

            /*
             This code produces the following output:

             passionfruit
            */

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.

            string fruit2 = null;

            try
            {
                fruit2 = fruits.Single(fruit => fruit.Length > 15);
            }
            catch (System.InvalidOperationException)
            {
                Console.WriteLine(@"The collection does not contain exactly 
                                one element whose length is greater than 15.");
            }

            Console.WriteLine(fruit2);

            // This code produces the following output: 
            // 
            // The collection does not contain exactly   
            // one element whose length is greater than 15.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Was this page helpful?
(1500 characters remaining)
Thank you for your feedback
Show:
© 2014 Microsoft