Enumerable.Except(Of TSource) Method (IEnumerable(Of TSource), IEnumerable(Of TSource), IEqualityComparer(Of TSource))
Produces the set difference of two sequences by using the specified IEqualityComparer(Of T) to compare values.
Assembly: System.Core (in System.Core.dll)
<ExtensionAttribute> Public Shared Function Except(Of TSource) ( first As IEnumerable(Of TSource), second As IEnumerable(Of TSource), comparer As IEqualityComparer(Of TSource) ) As IEnumerable(Of TSource)
Parameters
- first
-
Type:
System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) whose elements that are not also in second will be returned.
- second
-
Type:
System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) whose elements that also occur in the first sequence will cause those elements to be removed from the returned sequence.
- comparer
-
Type:
System.Collections.Generic.IEqualityComparer(Of TSource)
An IEqualityComparer(Of T) to compare values.
Return Value
Type: System.Collections.Generic.IEnumerable(Of TSource)A sequence that contains the set difference of the elements of two sequences.
Type Parameters
- TSource
The type of the elements of the input sequences.
| Exception | Condition |
|---|---|
| ArgumentNullException | first or second is null. |
The following example shows how to implement an equality comparer that can be used in the Except(Of TSource) 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 sequences of Product objects in the Except(Of TSource) method, as shown in the following example.
Dim fruits1() As Product = {New Product With {.Name = "apple", .Code = 9}, New Product With {.Name = "orange", .Code = 4}, New Product With {.Name = "lemon", .Code = 12}} Dim fruits2() As Product = {New Product With {.Name = "apple", .Code = 9}} ' Get all the elements from the first array ' except for the elements from the second array. Dim except = fruits1.Except(fruits2, New ProductComparer()) For Each product In except Console.WriteLine(product.Name & " " & product.Code) Next ' This code produces the following output: ' ' orange 4 ' lemon 12
Available since 8
.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