using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        List<Tuple<string, DateTime>> variantsToBeUpdated = new List<Tuple<string, DateTime>>();

        variantsToBeUpdated.Add(new Tuple<string, DateTime>("12345", new DateTime(2019, 2, 3)));

        variantsToBeUpdated.Add(new Tuple<string, DateTime>("12345", new DateTime(2018, 2, 3)));

        variantsToBeUpdated.Add(new Tuple<string, DateTime>("45678", new DateTime(2019, 2, 3)));

        variantsToBeUpdated.Add(new Tuple<string, DateTime>("45678", new DateTime(2015, 2, 3)));

        variantsToBeUpdated.Add(new Tuple<string, DateTime>("6666", new DateTime(2015, 2, 3)));

        variantsToBeUpdated.Add(new Tuple<string, DateTime>("6666", new DateTime(2018, 2, 3)));

        var filteredVariantsToBeUpdated = variantsToBeUpdated.GroupBy(x => x.Item1).Select(x => new {x.Key, Values = x.Select(item => new {item.Item2})});

        var filteredVariantsToBeUpdated2 = variantsToBeUpdated.GroupBy(x => x.Item1).Select(g => g.OrderByDescending(x => x.Item2).FirstOrDefault());

        foreach (var f in filteredVariantsToBeUpdated2) 

        {

            Console.WriteLine(f);

        }

    }

}