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


Determines whether two sequences are equal by comparing their elements by using a specified IEqualityComparer<T>.

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

public static bool SequenceEqual<TSource>(
	this IEnumerable<TSource> first,
	IEnumerable<TSource> second,
	IEqualityComparer<TSource> comparer


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

An IEnumerable<T> to compare to second.

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

An IEnumerable<T> to compare to the first sequence.

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

An IEqualityComparer<T> to use to compare elements.

Return Value

Type: System.Boolean

true if the two source sequences are of equal length and their corresponding elements compare equal according to comparer; otherwise, false.

Type Parameters


The type of the elements of the input sequences.

Exception Condition

first or second is null.

The SequenceEqual<TSource>(IEnumerable<TSource>, IEnumerable<TSource>, IEqualityComparer<TSource>) method enumerates the two source sequences in parallel and compares corresponding elements by using the specified IEqualityComparer<T>. If comparer is null, the default equality comparer, Default, is used to compare elements.

The following example shows how to implement an equality comparer that can be used in the SequenceEqual<TSource>(IEnumerable<TSource>, IEnumerable<TSource>, IEqualityComparer<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 SequenceEqual<TSource>(IEnumerable<TSource>, IEnumerable<TSource>, IEqualityComparer<TSource>) method, as shown in the following example.

Product[] storeA = { new Product { Name = "apple", Code = 9 }, 
                       new Product { Name = "orange", Code = 4 } };

Product[] storeB = { new Product { Name = "apple", Code = 9 }, 
                       new Product { Name = "orange", Code = 4 } };

bool equalAB = storeA.SequenceEqual(storeB, new ProductComparer());

Console.WriteLine("Equal? " + equalAB);

    This code produces the following output:

    Equal? True

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
Return to top