using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

            var myList = new List<Tuple<double, double, double, string, string, string>>

            {

                new Tuple<double, double, double, string, string, string>(10, 10, 11, "a", "b", "c"),

                new Tuple<double, double, double, string, string, string>(10, 10, 11, "x", "y", "z"),

                new Tuple<double, double, double, string, string, string>(12, 10, 11, "x", "y", "z")

            };

​

            var result = myList.GroupBy(x => new {x.Item1, x.Item2, x.Item3})

                .Select(x => x.First())

                .ToList();

​

            foreach (var tuple in result)

            {

                Console.WriteLine(tuple);

            }

    }

}