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Enumerable.SingleOrDefault(Of TSource) Method (IEnumerable(Of TSource), Func(Of 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
Assembly:  System.Core (in System.Core.dll)

'Declaration
<ExtensionAttribute> _
Public Shared Function SingleOrDefault(Of TSource) ( _
	source As IEnumerable(Of TSource), _
	predicate As Func(Of TSource, Boolean) _
) As TSource

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Collections.Generic.IEnumerable(Of TSource)

An IEnumerable(Of T) to return a single element from.

predicate
Type: System.Func(Of 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(Of 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 Nothing.

The default value for reference and nullable types is Nothing.

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

' Create an array of strings. 
Dim fruits() As String = _
    {"apple", "banana", "mango", "orange", "passionfruit", "grape"}

' Get the single item in the array whose length is > 10. 
Dim fruit1 As String = _
    fruits.SingleOrDefault(Function(fruit) fruit.Length > 10)

' Display the result.
MsgBox("First array: " & fruit1)

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

        ' Get the single item in the array whose length is > 15. 
        Dim fruit2 As String = _
            fruits.SingleOrDefault(Function(fruit) fruit.Length > 15)

        ' Display the result. 
        Dim output As String = _
            IIf(String.IsNullOrEmpty(fruit2), "No single item found", fruit2)
        MsgBox("Second array: " & output)

        ' This code produces the following output: 
        
        ' First array: passionfruit 
        ' Second array: No single item found

.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

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, 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.

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