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.NET Framework Class Library
EnumerableExceptTSource Method (IEnumerableTSource, IEnumerableTSource, IEqualityComparerTSource)

Produces the set difference of two sequences by using the specified IEqualityComparerT to compare values.

Namespace:   System.Linq
Assemblies:   System.Linq (in System.Linq.dll)
  System.Core (in System.Core.dll)
Syntax
<[%$TOPIC/bb336390_en-us_VS_110_2_0_0_0_0%]> _
Public Shared Function Except(Of TSource) ( _
	first As [%$TOPIC/bb336390_en-us_VS_110_2_0_0_0_1%](Of TSource), _
	second As [%$TOPIC/bb336390_en-us_VS_110_2_0_0_0_2%](Of TSource), _
	comparer As [%$TOPIC/bb336390_en-us_VS_110_2_0_0_0_3%](Of TSource) _
) As [%$TOPIC/bb336390_en-us_VS_110_2_0_0_0_4%](Of TSource)
public static [%$TOPIC/bb336390_en-us_VS_110_2_0_1_0_0%]<TSource> Except<TSource>(
	this [%$TOPIC/bb336390_en-us_VS_110_2_0_1_0_1%]<TSource> first,
	[%$TOPIC/bb336390_en-us_VS_110_2_0_1_0_2%]<TSource> second,
	[%$TOPIC/bb336390_en-us_VS_110_2_0_1_0_3%]<TSource> comparer
)
[[%$TOPIC/bb336390_en-us_VS_110_2_0_2_0_0%]]
public:
generic<typename TSource>
static [%$TOPIC/bb336390_en-us_VS_110_2_0_2_0_1%]<TSource>^ Except(
	[%$TOPIC/bb336390_en-us_VS_110_2_0_2_0_2%]<TSource>^ first, 
	[%$TOPIC/bb336390_en-us_VS_110_2_0_2_0_3%]<TSource>^ second, 
	[%$TOPIC/bb336390_en-us_VS_110_2_0_2_0_4%]<TSource>^ comparer
)
static member Except : 
        first:[%$TOPIC/bb336390_en-us_VS_110_2_0_3_0_0%]<'TSource> * 
        second:[%$TOPIC/bb336390_en-us_VS_110_2_0_3_0_1%]<'TSource> * 
        comparer:[%$TOPIC/bb336390_en-us_VS_110_2_0_3_0_2%]<'TSource> -> [%$TOPIC/bb336390_en-us_VS_110_2_0_3_0_3%]<'TSource> 
JScript does not support generic types or methods.

Type Parameters

TSource

The type of the elements of the input sequences.

Parameters

first
Type: System.Collections.GenericIEnumerableTSource

An IEnumerableT whose elements that are not also in second will be returned.

second
Type: System.Collections.GenericIEnumerableTSource

An IEnumerableT whose elements that also occur in the first sequence will cause those elements to be removed from the returned sequence.

comparer
Type: System.Collections.GenericIEqualityComparerTSource

An IEqualityComparerT to compare values.

Return Value

Type: System.Collections.GenericIEnumerableTSource
A sequence that contains the set difference of the elements of two sequences.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerableTSource. 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).
Exceptions
ExceptionCondition
ArgumentNullException

first or second is .

Remarks

If comparer is , the default equality comparer, Default, is used to compare values.

Examples

The following example shows how to implement an equality comparer that can be used in the Except 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
public class Product
{
    public string Name { get; set; }
    public int Code { get; set; }
}

// Custom comparer for the Product class 
class ProductComparer : IEqualityComparer<Product>
{
    // Products are equal if their names and product numbers are equal. 
    public bool Equals(Product x, Product y)
    {

        //Check whether the compared objects reference the same data. 
        if (Object.ReferenceEquals(x, y)) return true;

        //Check whether any of the compared objects is null. 
        if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
            return false;

        //Check whether the products' properties are equal. 
        return x.Code == y.Code && x.Name == y.Name;
    }

    // If Equals() returns true for a pair of objects  
    // then GetHashCode() must return the same value for these objects. 

    public int GetHashCode(Product product)
    {
        //Check whether the object is null 
        if (Object.ReferenceEquals(product, null)) return 0;

        //Get hash code for the Name field if it is not null. 
        int hashProductName = product.Name == null ? 0 : product.Name.GetHashCode();

        //Get hash code for the Code field. 
        int hashProductCode = product.Code.GetHashCode();

        //Calculate the hash code for the product. 
        return hashProductName ^ hashProductCode;
    }

}

After you implement this comparer, you can use sequences of Product objects in the Except 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
        Product[] fruits1 = { new Product { Name = "apple", Code = 9 }, 
                               new Product { Name = "orange", Code = 4 },
                                new Product { Name = "lemon", Code = 12 } };

        Product[] fruits2 = { new Product { Name = "apple", Code = 9 } };

        //Get all the elements from the first array 
        //except for the elements from the second array.

        IEnumerable<Product> except =
            fruits1.Except(fruits2, new ProductComparer());

        foreach (var product in except)
            Console.WriteLine(product.Name + " " + product.Code);

        /*
          This code produces the following output:

          orange 4
          lemon 12
        */
Version Information

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8