LINQ vs キーブレイク

Program.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
  class Program
  {
    class Sales
    {
      public string Customer { get; set; }
      public string Product { get; set; }
      public decimal UnitPrice { get; set; }
      public int Quantity { get; set; }

      public override string ToString()
      {
        return string.Format("C:{0}, P:{1}, U:{2}, Q:{3}", Customer, Product, UnitPrice, Quantity);
      }
    }
    static void Main(string[] args)
    {
      var q = from i in Enumerable.Range(1, 100)
              from j in Enumerable.Range(1, 100)
              from k in Enumerable.Range(1, 10)
              select new Sales
              {
                Customer = string.Format("取引先{0:d2}", i),
                Product = string.Format("商品{0:d2}", j),
                UnitPrice = Convert.ToDecimal(j * 100),
                Quantity = k
              };
      var source = q.ToArray();

      const int times = 10;

      var linqTime = UsingLinq(times, source);
      var keyBreakTime = UsingKeyBreak(times, source);

      Console.WriteLine();

      Console.WriteLine("■LINQ:{0}", linqTime);
      Console.WriteLine("■Key Break:{0}", keyBreakTime);
    }

    private static decimal UsingLinq(int times, IEnumerable<Sales> source)
    {
      var sw = new Stopwatch();
      var totalTime = 0L;
      for (var i = 0; i < times; i++)
      {
        sw.Reset();
        sw.Start();
        var salesOfCustomers = source.GroupBy(x => x.Customer);

        foreach (var salesOfCustomer in salesOfCustomers)
        {
          var salesOfProducts = salesOfCustomer.GroupBy(x => (x.Product));
          foreach (var salesOfProduct in salesOfProducts)
          {
            foreach (var sales in salesOfProduct)
            {
              Console.WriteLine(sales);
            }
            Console.WriteLine("小計 P:{0}, {1}, {2}", salesOfProduct.Key, salesOfProduct.Sum(x => x.Quantity),
              salesOfProduct.Sum(x => x.UnitPrice * x.Quantity));
          }
          Console.WriteLine("大計 C:{0}, {1}, {2}", salesOfCustomer.Key, salesOfCustomer.Sum(x => x.Quantity),
            salesOfCustomer.Sum(x => x.UnitPrice * x.Quantity));
        }
        Console.WriteLine("総計 {0}, {1}", source.Sum(x => x.Quantity), source.Sum(x => x.UnitPrice * x.Quantity));
        sw.Stop();

        Console.WriteLine(sw.ElapsedMilliseconds);
        totalTime += sw.ElapsedMilliseconds;
      }
      var averageTime = (decimal)totalTime / times;
      return averageTime;
    }

    private static decimal UsingKeyBreak(int times, IEnumerable<Sales> source)
    {
      var sw = new Stopwatch();
      var totalTime = 0L;
      for (var i = 0; i < times; i++)
      {
        sw.Reset();
        sw.Start();

        var oldCustomer = "";
        var newCustomer = "";
        var oldProduct = "";
        var newProduct = "";

        var totalQuantity = 0L;
        var totalPrice = 0m;
        var totalCustomerQuantity = 0L;
        var totalCustomerPrice = 0m;
        var totalProductQuantity = 0L;
        var totalProductPrice = 0m;

        foreach (var sales in source)
        {
          if (oldCustomer == "")
          {
            oldCustomer = sales.Customer;
            oldProduct = sales.Product;
          }
          newCustomer = sales.Customer;
          newProduct = sales.Product;

          if (oldCustomer != newCustomer || oldProduct != newProduct)
          {
            Console.WriteLine("小計 P:{0}, {1}, {2}", oldProduct, totalProductQuantity, totalProductPrice);
            totalProductQuantity = 0L;
            totalProductPrice = 0m;

            oldProduct = newProduct;
          }

          if (oldCustomer != newCustomer)
          {
            Console.WriteLine("大計 P:{0}, {1}, {2}", oldCustomer, totalCustomerQuantity, totalCustomerPrice);
            totalCustomerQuantity = 0L;
            totalCustomerPrice = 0m;

            oldCustomer = newCustomer;
          }

          totalProductQuantity += sales.Quantity;
          totalProductPrice += sales.UnitPrice * sales.Quantity;
          totalCustomerQuantity += sales.Quantity;
          totalCustomerPrice += sales.UnitPrice * sales.Quantity;
          totalQuantity += sales.Quantity;
          totalPrice += sales.UnitPrice * sales.Quantity;

          Console.WriteLine(sales);
        }
        Console.WriteLine("小計 P:{0}, {1}, {2}", oldProduct, totalProductQuantity, totalProductPrice);
        Console.WriteLine("大計 P:{0}, {1}, {2}", oldCustomer, totalCustomerQuantity, totalCustomerPrice);
        Console.WriteLine("総計 {0}, {1}", totalQuantity, totalPrice);

        sw.Stop();

        Console.WriteLine(sw.ElapsedMilliseconds);
        totalTime += sw.ElapsedMilliseconds;
      }
      var averageTime = (decimal)totalTime / times;
      return averageTime;
    }
  }
}