using System;

using System.Collections.Generic;

using System.Linq;

​

using System.Data;

using FastMember;

​

public class Program

{

    public static void Main()

    {

        var years = Enumerable.Range(2015,2);

        var months = Enumerable.Range(1,5);

        var dates =     (from y in years

                        from m in months

                        select new DateTime(y,m,1) // public DateTime (int year, int month, int day);

                         ).ToList();

        var ordered = dates.OrderByDescending(d=> d.Year).ThenBy(d=> d.Month);      

        ordered.Select(x=> $"{x.Year}/{x.Month}").Dump();

        var ordered2 = dates.OrderByDescending(d=> d.Year).ThenByDescending(d=> d.Month);   

        ordered2.Select(x=> $"{x.Year}/{x.Month}").Dump();

​

        // With Data Table.

        DataTable table = new DataTable();

        using(var reader = ObjectReader.Create(dates, "Date")) {

            table.Load(reader);

        }

        var orderedWithDT = table.AsEnumerable().OrderByDescending(x => x.Field<DateTime>("Date").Year).ThenBy(y => y.Field<DateTime>("Date").Month);       

        orderedWithDT.SelectMany(x=> x.ItemArray).Dump();

    }

}