using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

         List<Order> orders = new List<Order>

           {

               new Order { UserId = 1, OrderId =1, Email = "blah1", PostCode = 111, Country = "au" },

               new Order { UserId = 2, OrderId =1, Email = "blah2", PostCode = 111, Country = "au" },

               new Order { UserId = 3, OrderId =2, Email = "blah1", PostCode = 111, Country = "au" },

               new Order { UserId = 4, OrderId =2, Email = "blah2", PostCode = 111, Country = "au" },

               new Order { UserId = 5, OrderId =3, Email = "blah3", PostCode = 111, Country = "nz" },

               new Order { UserId = 6, OrderId =3, Email = "blah3", PostCode = 111, Country = "nz" },

               new Order { UserId = 7, OrderId =5, Email = "blah5", PostCode = 111, Country = "au" },

           };

​

            var query = from ord in orders

                        group ord by new { ord.Country, ord.PostCode } into g

                        select new

                            {

                                Country = g.Key.Country,

                                PostCode = g.Key.PostCode,

                                Orders = g.GroupBy(x => x.OrderId)

                                          .GroupBy(i => i.Count() > 1 ?

                                              new { OrderID = i.Key, Email = default(string) }

                                              : new { OrderID = default(int), i.First().Email })

                                          .Select(o => o.Count() == 1 ?

                                               new { o.Key, Orders = o.First().ToList() }

                                               : new { o.Key, Orders = o.Select(z => z.First()).ToList() })

                            };

​

​

            foreach (var data in query)

            {

                Console.WriteLine("Country : {0}, PostCode : {1}", data.Country, data.PostCode);

                foreach (var ord in data.Orders)

                {

                    Console.WriteLine(String.IsNullOrEmpty(ord.Key.Email) ? "OrderID : " + ord.Key.OrderID.ToString() : "Email: " + ord.Key.Email);

                    foreach (var ords in ord.Orders)

                    {

                        Console.WriteLine("UserId : {0}", ords.UserId);

                    }

                    Console.WriteLine();

                }

                Console.WriteLine("-----");

            }

    }

}

​

public class Order

    {

        public int UserId { get; set; }

        public int OrderId { get; set; }

        public string Email { get; set; }

        public int PostCode { get; set; }

        public string Country { get; set; }

    }