Group by Example, C#

Group by Example

//Title of this code
//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            //Your code goes here
            
            var orders = new List<Order>();
            orders.Add(new Order(){Id=1, Product = "1"});
            orders.Add(new Order(){Id=2, Product = "2"});
            orders.Add(new Order(){Id=3, Product = "1"});
            orders.Add(new Order(){Id=4, Product = "3"});
            orders.Add(new Order(){Id=5, Product = "3"});
            orders.Add(new Order(){Id=6, Product = "1"});
            orders.Add(new Order(){Id=7, Product = "1"});
            orders.Add(new Order(){Id=8, Product = "1"});
            
            var groupedOrders = orders.GroupBy(o => o.Product); // Returns an IGrouping where key is the id and the value is IEnumerable of orders 
            var sortedGroups = groupedOrders.OrderByDescending(g => g.Count()); // Sorts the groups descending by count of the IEnumerable of orders  
            var projectedOrders = sortedGroups.Select(x => new CustomerOrders(){OrderId = x.First().Id, // Projects each of the groups into a new CustomerOrders
                                                  Product = x.First().Product, 
                                                  Count = x.Count()});
            
            System.Console.Write(projectedOrders.Last().OrderId);
        }
        
        
        public class Customers
        {
            public Guid Id { get; set; }
            public string FirstName{ get; set; }
            public string LastName{ get; set; }
        }
        
        public class Order
        {
            public int Id { get; set; }
            public Guid CustomerId { get; set; }
            public string Product { get; set; }
            public DateTime Date { get; set; }
        }
        
        public class CustomerOrders
        {
            public int OrderId { get; set; }
            public string Product { get; set; }
            public int Count { get; set; }
        }
        
    }
}


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