using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        var authors = new Author[]

        {

        new Author

        {

        FirstName = "Joseph", Surname = "Albahari"

        }

​

        , new Author

        {

        FirstName = "Ben", Surname = "Albahari"

        }

​

        , new Author

        {

        FirstName = "Andrew", Surname = "Troelsen"

        }

​

        , new Author

        {

        FirstName = "Joseph", Surname = "Albahari"

        }

​

        , new Author

        {

        FirstName = "Ben", Surname = "Albahari"

        }

​

         }

​

        ;

        SimpleDistinct();

        DistinctAnonymous(authors);

        DistinctAnonymousCastBack(authors);

        DistinctByGrouping(authors);

        DistinctByComparer(authors);

        DistinctByExtension(authors);

        DistinctByExtension2(authors);

    }

​

​

    private static void PrintAuthors(IEnumerable<Author> authors)

    {

        Console.WriteLine("AUTHORS:");

        foreach (var author in authors)

            Console.WriteLine("{0} {1}", author.FirstName, author.Surname);

    }

​

    private static void SimpleDistinct()

    {

        var numbers = new int[]

        {

        1, 2, 3, 1, 2, 3, 4, 5

        }

​

        ;

        var cleanedNumbers = numbers.Distinct();

        foreach (var number in cleanedNumbers)

            Console.WriteLine(number);

    }

​

    private static void DistinctAnonymous(IEnumerable<Author> authors)

    {

        var cleanedAuthors = authors.Select(a => new

        {

        FirstName = a.FirstName, Surname = a.Surname

        }

​

        ).Distinct();

        foreach (var author in authors)

            Console.WriteLine("{0} {1}", author.FirstName, author.Surname);

    }

​

    private static void DistinctAnonymousCastBack(IEnumerable<Author> authors)

    {

        var cleanedAuthors = authors.Select(a => new

        {

        FirstName = a.FirstName, Surname = a.Surname

        }

​

        ).Distinct().Select(a => new Author

        {

        FirstName = a.FirstName, Surname = a.Surname

        }

​

        );

        PrintAuthors(cleanedAuthors);

    }

​

    private static void DistinctByGrouping(IEnumerable<Author> authors)

    {

        var cleanedAuthors = authors.GroupBy(a => new

        {

        a.FirstName, a.Surname

        }

​

        ).Select(g => g.First());

        PrintAuthors(cleanedAuthors);

    }

​

    private static void DistinctByComparer(IEnumerable<Author> authors)

    {

        var cleanedAuthors = authors.Distinct(new AuthorComparer());

        PrintAuthors(cleanedAuthors);

    }

​

    private static void DistinctByExtension(IEnumerable<Author> authors)

    {

        var cleanedAuthors = authors.Distinct(a => a.Surname);

        PrintAuthors(cleanedAuthors);

    }

​

    private static void DistinctByExtension2(IEnumerable<Author> authors)

    {

        var cleanedAuthors = authors.Distinct(a => new

        {

        a.FirstName, a.Surname

        }

​

        );

        PrintAuthors(cleanedAuthors);

    }

}

​

public class AuthorComparer : IEqualityComparer<Author>

{

    public bool Equals(Author x, Author y)

    {

        return x.FirstName.Equals(y.FirstName) && x.Surname.Equals(y.Surname);

    }

​

    public int GetHashCode(Author obj)

    {

        unchecked

        {

            int hash = 17;

            hash = hash * 23 + obj.FirstName.GetHashCode();

            hash = hash * 23 + obj.Surname.GetHashCode();

            return hash;

        }

    }

}

​

public static class LinqExtension

{

    public static IEnumerable<T> Distinct<T>(this IEnumerable<T> input, Func<T, object> keySelector)

    {

        return input.Distinct(new ByKeyComparer<T>(keySelector));

    }

}

​

public class ByKeyComparer<T> : IEqualityComparer<T>

{

    private readonly Func<T, object> keySelector;

    public ByKeyComparer(Func<T, object> keySelector)

    {

        this.keySelector = keySelector;

    }

​

    public bool Equals(T x, T y)

    {

        return this.keySelector(x).Equals(this.keySelector(y));

    }

​

    public int GetHashCode(T obj)

    {

        return this.keySelector(obj).GetHashCode();

    }

}

​

public class Author

{

    public int Id

    {

        get;

        set;

    }

​

    public string FirstName

    {

        get;

        set;

    }

​

    public string Surname

    {

        get;

        set;

    }

}