// Distinct not working with LINQ to Objects

​

// see: https://stackoverflow.com/a/1365771/1016343

​

using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        // first example: Distinct does not work

        var authors1 = new List<Author>() {

            new Author() { FirstName="John", LastName="Doe" },

            new Author() { FirstName="John", LastName="Doe" },

            new Author() { FirstName="Jane", LastName="Doe" },

            new Author() { FirstName="Jane", LastName="Doe" }

        };

        authors1.Distinct().Dump();

​

        // second example: Distinct works as expected

        var authors2 = new List<DistinctAuthor>() {

            new DistinctAuthor() { FirstName="John", LastName="Doe" },

            new DistinctAuthor() { FirstName="John", LastName="Doe" },

            new DistinctAuthor() { FirstName="Jane", LastName="Doe" },

            new DistinctAuthor() { FirstName="Jane", LastName="Doe" }

        };

        authors2.Distinct().Dump();

    }

}

​

// first example: Distinct does not work

public class Author

{

    public string FirstName { get; set; }

    public string LastName { get; set; }

}

​

​

// second example: Distinct works as expected

public class DistinctAuthor : IEquatable<DistinctAuthor>

{

    public string FirstName { get; set; }

    public string LastName { get; set; }

    public bool Equals(DistinctAuthor other)

    {

        if (FirstName == other.FirstName && LastName == other.LastName)

            return true;

        return false;

    }

    public override int GetHashCode()

    {

        int hashFirstName = FirstName == null ? 0 : FirstName.GetHashCode();

        int hashLastName = LastName == null ? 0 : LastName.GetHashCode();

        return hashFirstName ^ hashLastName;

    }

}

​

​

​