using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var items = new List<Foo>

        {

            new Foo{MyProperty = 1},

            new Foo{MyProperty = 2},

            new Foo{MyProperty = 1}

        };

        var enumerable = items.DistinctBy(f => f.MyProperty);

        Console.WriteLine("Count: {0}", enumerable.Count());

        Console.WriteLine("Count: {0}", enumerable.Count());

    }

}

​

public class Foo

{

   public int MyProperty { get; set; }

}

​

public static class Extensions

{

   public static IEnumerable<T> DistinctBy<T, TKey>(this IEnumerable<T> items, Func<T, TKey> property)

   {

      if (items == null || property == null)

         return Enumerable.Empty<T>();

​

​

      var known = new HashSet<TKey>();

      return items.Where(element => known.Add(property(element)));

   }

}