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

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

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).

ExceptionCondition
ArgumentNullException

source or predicate is null.

The default value for reference and nullable types is null.

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!
            */

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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