Enumerable.Except<TSource> Method (IEnumerable<TSource>, IEnumerable<TSource>)

Note
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Produces the set difference of two sequences by using the default equality comparer to compare values.

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

Syntax

C++

JScript

PowerShell

<ExtensionAttribute>
Public Shared Function Except(Of TSource) (
	first As IEnumerable(Of TSource),
	second As IEnumerable(Of TSource)
) As IEnumerable(Of TSource)

Parameters

first: Type: System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> whose elements that are not also in second will be returned.

second: Type: System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> whose elements that also occur in the first sequence will cause those elements to be removed from the returned sequence.

Return Value

Type: System.Collections.Generic.IEnumerable<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.

Exceptions

Exception	Condition
ArgumentNullException	first or second is null.

Remarks

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 set difference of two sets is defined as the members of the first set that do not appear in the second set.

Note
This method returns those elements in first that do not appear in second. It does not also return those elements in second that do not appear in first.

The default equality comparer, Default, is used to compare values of the types that implement the IEqualityComparer<T> generic interface. To compare a custom data type, you need to implement this interface and provide your own GetHashCode and Equals methods for the type.

Examples

The following code example demonstrates how to use the Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) method to compare two sequences of numbers and return elements that appear only in the first sequence.

C++

JScript

PowerShell

' Create two arrays of doubles.
Dim numbers1() As Double = { 2.0, 2.0, 2.1, 2.2, 2.3, 2.3, 2.4, 2.5 }
Dim numbers2() As Double = {2.2}

' Select the elements from the first array that are not
' in the second array.
Dim onlyInFirstSet As IEnumerable(Of Double) = numbers1.Except(numbers2)

Dim output As New System.Text.StringBuilder
For Each number As Double In onlyInFirstSet
    output.AppendLine(number)
Next

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

' This code produces the following output:
'
' 2
' 2.1
' 2.3
' 2.4
' 2.5

If you want to compare sequences of objects of some custom data type, you have to implement the IEqualityComparer<T> generic interface in a helperclass. The following code example shows how to implement this interface in a custom data type and provide GetHashCode and Equals methods.

C++

JScript

PowerShell

No code example is currently available or this language may not be supported.

After you implement this interface, you can use sequences of ProductA objects in the Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) method, as shown in the following example.

C++

JScript

PowerShell

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)

For Each product In except
    Console.WriteLine(product.Name & " " & product.Code)
Next

' This code produces the following output:
'
' orange 4
' lemon 12

Version Information

Universal Windows Platform
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