C# Online Compiler | .NET Fiddle

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;
	}
}

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