SingleOrDefault(TSource) Method (IEnumerable(TSource), Func(TSource, Boolean))

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)

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

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.

Type Parameters

TSource

The type of the elements of source.

Exception Condition
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(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

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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