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

.NET Framework 4.5

Returns the only element of a sequence that satisfies a specified condition or a default value if no such element exists; this method throws an exception if more than one element satisfies the condition.

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

Syntax

C++

public static TSource SingleOrDefault<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 the condition, or default(TSource) if no such element is found.

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).

Exceptions

Exception	Condition
ArgumentNullException	source or predicate is null.

Remarks

The default value for reference and nullable types is null.

Examples

The following code example demonstrates how to use SingleOrDefault<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.SingleOrDefault(fruit => fruit.Length > 10);

            Console.WriteLine(fruit1);

            /*
             This code produces the following output:

             passionfruit
            */

The following code example demonstrates that SingleOrDefault<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) returns a default value when the sequence does not contain exactly one element that satisfies the condition.

            string fruit2 =
                fruits.SingleOrDefault(fruit => fruit.Length > 15);

            Console.WriteLine(
                String.IsNullOrEmpty(fruit2) ? "No such string!" : fruit2);

            /*
             This code produces the following output:

             No such string!
            */

Version Information

.NET Framework

Supported in: 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

Platforms

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.

Reference

Enumerable Class

SingleOrDefault Overload

System.Linq Namespace

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