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


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)

public static IEnumerable<TSource> Except<TSource>(
	this IEnumerable<TSource> first,
	IEnumerable<TSource> second


Type: System.Collections.Generic.IEnumerable<TSource>

An IEnumerable<T> whose elements that are not also in second will be returned.

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


The type of the elements of the input sequences.

Exception Condition

first or second is null.

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.


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.

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.

double[] numbers1 = { 2.0, 2.0, 2.1, 2.2, 2.3, 2.3, 2.4, 2.5 };
double[] numbers2 = { 2.2 };

IEnumerable<double> onlyInFirstSet = numbers1.Except(numbers2);

foreach (double number in onlyInFirstSet)

 This code produces the following output:


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.

public class ProductA
    public string Name { get; set; }
    public int Code { get; set; }

public class ProductComparer : IEqualityComparer<ProductA>

    public bool Equals(ProductA x, ProductA y)
        //Check whether the objects are the same object. 
        if (Object.ReferenceEquals(x, y)) return true;

        //Check whether the products' properties are equal. 
        return x != null && y != null && x.Code.Equals(y.Code) && x.Name.Equals(y.Name);

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

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

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

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.

ProductA[] fruits1 = { new ProductA { Name = "apple", Code = 9 }, 
                       new ProductA { Name = "orange", Code = 4 },
                        new ProductA { Name = "lemon", Code = 12 } };

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

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

IEnumerable<ProductA> except =

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

  This code produces the following output:

  orange 4
  lemon 12

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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