using System;

using System.Linq;

using System.Collections.Generic;

​

// see: https://stackoverflow.com/a/24952248/1016343

public static class Extensions

{

    public static IEnumerable<T> MyDistinct<T, V>(this IEnumerable<T> query,

                                                    Func<T, V> f, 

                                                    Func<IGrouping<V,T>,T> h=null)

    {

        if (h==null) h=(x => x.First());

        return query.GroupBy(f).Select(h);

    }

    public static IEnumerable<T> MyDistinct2<T, V>(this IEnumerable<T> query,

                                                Func<T, V> f,

                                                Func<T,bool> h=null)

    {

        if (h == null) h = (y => true);

        return query.GroupBy(f).Select(x=>x.FirstOrDefault(h));

    }

}

​

public class MyObject

{

    public string Name;

    public string Code;

}

public class Program

{

    public static void Main()

    {

        MyObject[] _myObject = {

            new MyObject() { Name = "Test1", Code = "T"},

            new MyObject() { Name = "Test2", Code = "Q"},

            new MyObject() { Name = "Test2", Code = "T"},

            new MyObject() { Name = "Test5", Code = "Q"}

        };

        Console.WriteLine("First example");

        var myQuery=(from x in _myObject select x).MyDistinct(d => d.Code);

        myQuery.Dump();

        Console.WriteLine(); Console.WriteLine(); Console.WriteLine("Second example");

        var myQuery2 = (from x in _myObject select x).MyDistinct(d => d.Name,

                            x=>x.FirstOrDefault(y=>y.Name.Contains("1") || y.Name.Contains("2"))

                        );

        myQuery2.Dump();

        Console.WriteLine(); Console.WriteLine(); Console.WriteLine("Third example");

        var myQuery3 = (from x in _myObject select x).MyDistinct2(d => d.Name,

                            y => y.Name.Contains("1") || y.Name.Contains("2")

                        );

        myQuery3.Dump();

    }

}