using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        List<MonthlySales> col1 = new List<MonthlySales>

            {

                new MonthlySales { Year = 2014, Month= "June", Sales = new Dictionary<string,double> { { "Prod1", 123 }, { "Prod2", 23 } } },

                new MonthlySales { Year = 2014, Month= "Aug", Sales = new Dictionary<string,double> { { "Prod3", 12 }, { "Prod4", 55 } } },

            };

​

            List<MonthlySales> col2 = new List<MonthlySales>

            {

                new MonthlySales { Year = 2014, Month= "June", Sales = new Dictionary<string,double> { { "Prod3", 12 }, { "Prod2", 10 } } },

                new MonthlySales { Year = 2014, Month= "Aug", Sales = new Dictionary<string,double> { { "Prod2", 10 }, { "Prod4", 50 } } },

            };

​

​

​

            List<MonthlySales> result = col1.Concat(col2)

                               .SelectMany(x => x.Sales, (monthhlySalesObj, sale) => new { monthhlySalesObj.Year, monthhlySalesObj.Month, sale })

                               .GroupBy(x => new { x.Year, x.Month, ProductName = x.sale.Key })

                               .Select(x => new MonthlySales

                                {

                                    Year = x.Key.Year,

                                    Month = x.Key.Month,

                                    Sales = new Dictionary<string, double> { { x.Key.ProductName, x.Sum(z => z.sale.Value) } }

                                }).ToList();

​

            foreach (var item in result)

            {

                Console.WriteLine("Year: {0}", item.Year);

                Console.WriteLine("Month: {0}", item.Month);

                foreach (var sale in item.Sales)

                {

                    Console.WriteLine("Product Name: {0}", sale.Key);

                    Console.WriteLine("Sales Price: {0}", sale.Value);

                }

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

            }

    }

}

​

public class MonthlySales

        {

            public int Year { get; set; }

            public string Month { get; set; }

            public Dictionary<string, double> Sales { get; set; }

        }