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.

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.
outputBlock.Text &= "First array: " & fruit1 & vbCrLf


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)
      outputBlock.Text &= "Second array: " & output & vbCrLf

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



Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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