using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        List<Tuple<int, int>> list =  new  List<Tuple<int, int>>()

        {

            new Tuple<int, int>(1,12),

            new Tuple<int, int>(1,2),

            new Tuple<int, int>(1,18),

            new Tuple<int, int>(1,12),

            new Tuple<int, int>(2,12),  

        };

        Console.WriteLine("Distinct() on both values");

        foreach(var item in list.Distinct().ToList())

        {

            Console.WriteLine(item);

        }       

        //This is the code you are looking for

        Console.WriteLine("GroupBy() second value");

        foreach(var item in list.GroupBy(x => x.Item2).Select(x => x.First()))

        {

            Console.WriteLine(item);

        }

    }

}