Enumerable.Distinct(Of TSource) Method (IEnumerable(Of TSource), IEqualityComparer(Of TSource))
Returns distinct elements from a sequence by using a specified IEqualityComparer(Of T) to compare values.
Assembly: System.Core (in System.Core.dll)
'Declaration <ExtensionAttribute> _ Public Shared Function Distinct(Of TSource) ( _ source As IEnumerable(Of TSource), _ comparer As IEqualityComparer(Of TSource) _ ) As IEnumerable(Of TSource)
Type Parameters
- TSource
The type of the elements of source.
Parameters
- source
- Type: System.Collections.Generic.IEnumerable(Of TSource)
The sequence to remove duplicate elements from.
- comparer
- Type: System.Collections.Generic.IEqualityComparer(Of TSource)
An IEqualityComparer(Of T) to compare values.
Return Value
Type: System.Collections.Generic.IEnumerable(Of TSource)An IEnumerable(Of T) that contains distinct elements from the source sequence.
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).| Exception | Condition |
|---|---|
| ArgumentNullException | source is Nothing. |
This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.
The Distinct(Of TSource)(IEnumerable(Of TSource), IEqualityComparer(Of TSource)) method returns an unordered sequence that contains no duplicate values. If comparer is Nothing, the default equality comparer, Default, is used to compare values.
The following example shows how to implement an equality comparer that can be used in the Distinct method.
Public Class Product Public Property Name As String Public Property Code As Integer End Class ' Custom comparer for the Product class Public Class ProductComparer Implements IEqualityComparer(Of Product) Public Function Equals1( ByVal x As Product, ByVal y As Product ) As Boolean Implements IEqualityComparer(Of Product).Equals ' Check whether the compared objects reference the same data. If x Is y Then Return True 'Check whether any of the compared objects is null. If x Is Nothing OrElse y Is Nothing Then Return False ' Check whether the products' properties are equal. Return (x.Code = y.Code) AndAlso (x.Name = y.Name) End Function Public Function GetHashCode1( ByVal product As Product ) As Integer Implements IEqualityComparer(Of Product).GetHashCode ' Check whether the object is null. If product Is Nothing Then Return 0 ' Get hash code for the Name field if it is not null. Dim hashProductName = If(product.Name Is Nothing, 0, product.Name.GetHashCode()) ' Get hash code for the Code field. Dim hashProductCode = product.Code.GetHashCode() ' Calculate the hash code for the product. Return hashProductName Xor hashProductCode End Function End Class
After you implement this comparer, you can use a sequence of Product objects in the Distinct method, as shown in the following example.
Dim products() As Product = {New Product With {.Name = "apple", .Code = 9}, New Product With {.Name = "orange", .Code = 4}, New Product With {.Name = "apple", .Code = 9}, New Product With {.Name = "lemon", .Code = 12}} ' Exclude duplicates. Dim noduplicates = products.Distinct(New ProductComparer()) For Each product In noduplicates Console.WriteLine(product.Name & " " & product.Code) Next ' This code produces the following output: ' ' apple 9 ' orange 4 ' lemon 12 '
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.