C#

List<product> products = GetProductList();

  var categories =
     from p in products
     group p by p.Category into g
     select new { Category = g.Key, TotalUnitsInStock = g.Sum(p => p.UnitsInStock) };

  ObjectDumper.Write(categories);
</product>

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("IS IT WORKING!!");
            Console.ReadLine();
        }
    }
}