Except(TSource) Method (IEnumerable(TSource), IEnumerable(TSource), IEqualityComparer(TSource))

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


Produces the set difference of two sequences by using the specified IEqualityComparer<T> 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,
	IEqualityComparer<TSource> comparer


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.

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

An IEqualityComparer<T> to compare values.

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.

If comparer is null, 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 Except<TSource> method.

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<TSource> method, as shown in the following example.

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

Universal Windows Platform
Available since 4.5
.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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