Intersect(TSource) Method (IEnumerable(TSource), IEnumerable(TSource))

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


Produces the set intersection 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> Intersect<TSource>(
	this IEnumerable<TSource> first,
	IEnumerable<TSource> second


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

An IEnumerable<T> whose distinct elements that also appear in second will be returned.

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

An IEnumerable<T> whose distinct elements that also appear in the first sequence will be returned.

Return Value

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

A sequence that contains the elements that form the set intersection 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 intersection of two sets A and B is defined as the set that contains all the elements of A that also appear in B, but no other elements.

When the object returned by this method is enumerated, Intersect<TSource> enumerates first, collecting all distinct elements of that sequence. It then enumerates second, marking those elements that occur in both sequences. Finally, the marked elements are yielded in the order in which they were collected.

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 Intersect<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) to return the elements that appear in each of two sequences of integers.

int[] id1 = { 44, 26, 92, 30, 71, 38 };
int[] id2 = { 39, 59, 83, 47, 26, 4, 30 };

IEnumerable<int> both = id1.Intersect(id2);

foreach (int id in both)

 This code produces the following output:


If you want to compare sequences of objects of a custom data type, you have to implement the IEqualityComparer<T> generic interface in a helper class. 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 Intersect<TSource> method, as shown in the following example.

ProductA[] store1 = { new ProductA { Name = "apple", Code = 9 }, 
                       new ProductA { Name = "orange", Code = 4 } };

ProductA[] store2 = { new ProductA { Name = "apple", Code = 9 }, 
                       new ProductA { Name = "lemon", Code = 12 } };
// Get the products from the first array 
// that have duplicates in the second array.

IEnumerable<ProductA> duplicates =
    store1.Intersect(store2, new ProductComparer());

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

    This code produces the following output:
    apple 9

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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