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Queryable.Distinct(Of TSource) Method (IQueryable(Of TSource))

Returns distinct elements from a sequence by using the default equality comparer to compare values.

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

'Declaration
<ExtensionAttribute> _
Public Shared Function Distinct(Of TSource) ( _
	source As IQueryable(Of TSource) _
) As IQueryable(Of TSource)

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Linq.IQueryable(Of TSource)
The IQueryable(Of T) to remove duplicates from.

Return Value

Type: System.Linq.IQueryable(Of TSource)
An IQueryable(Of T) that contains distinct elements from source.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable(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 is Nothing.

The Distinct(Of TSource)(IQueryable(Of TSource)) method generates a MethodCallExpression that represents calling Distinct(Of TSource)(IQueryable(Of TSource)) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery(Of TElement)(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

The query behavior that occurs as a result of executing an expression tree that represents calling Distinct(Of TSource)(IQueryable(Of TSource)) depends on the implementation of the type of the source parameter. The expected behavior is that it returns an unordered sequence of the unique items in source.

The following code example demonstrates how to use Distinct(Of TSource)(IQueryable(Of TSource)) to return distinct elements from a sequence.


        Dim ages As List(Of Integer) = New List(Of Integer)(New Integer() {21, 46, 46, 55, 17, 21, 55, 55})

        Dim distinctAges As IEnumerable(Of Integer) = ages.AsQueryable().Distinct()

        Dim output As New System.Text.StringBuilder
        output.AppendLine("Distinct ages:")

        For Each age As Integer In distinctAges
            output.AppendLine(age)
        Next

        ' Display the output.
        MsgBox(output.ToString())

        ' This code produces the following output:
        '
        ' Distinct(ages)
        ' 21
        ' 46
        ' 55
        ' 17



.NET Framework

Supported in: 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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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