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  1.  
  2. using System;
  3. using System.Collections.Generic;
  4. using System.Diagnostics;
  5. using System.Linq;
  6.  
  7. public class EmployeeDto
  8. {
  9.     public int Id { get; set; }
  10.     public string Name { get; set; }
  11. }
  12.  
  13. public class EmployeeEntity
  14. {
  15.     public int Id { get; set; }
  16.     public string FullName { get; set; }
  17. }
  18.  
  19. class Program
  20. {
  21.     static void Main(string[] args)
  22.     {
  23.         List<object> o = new List<object>();
  24.         o.Add(new EmployeeDto { Id = 1, Name = "Bob" });
  25.         o.Add(null);
  26.         o.Add(new EmployeeDto { Id = 2, Name = "Foo" });
  27.         o.Add(null);
  28.         o.AddRange(AddMilionOfEmployees());
  29.  
  30.         Stopwatch sw = new Stopwatch();
  31.         //sw.Start();
  32.         //var employeeEntityList = MapList1(o);
  33.         //sw.Stop();
  34.         //Console.WriteLine("ElapsedTicks Solution 1 (OfType): " + sw.ElapsedTicks);
  35.  
  36.         //Console.WriteLine("--");
  37.  
  38.         //sw = new Stopwatch();
  39.         sw.Start();
  40.         var employeeEntityList2 = MapList2(o);
  41.         sw.Stop();
  42.         Console.WriteLine("ElapsedTicks Solution 2 (let): " + sw.ElapsedTicks);
  43.  
  44.         Console.ReadKey();
  45.     }
  46.  
  47.     private static IEnumerable<object> AddMilionOfEmployees()
  48.     {
  49.         for (int i = 0; i < 100000; i++) //ideone doesn't allow a million.. ¬¬
  50.         {
  51.             Random randNum = new Random();
  52.             yield return new EmployeeDto { Id = i, Name = String.Format("Employee{0}", i * randNum.Next()) };
  53.         }
  54.     }
  55.  
  56.     private static IEnumerable<EmployeeEntity> MapList1(List<object> o)
  57.     {
  58.         return
  59.             from i in o.OfType<EmployeeDto>()
  60.             select new EmployeeEntity
  61.             {
  62.                 Id = i.Id,
  63.                 FullName = i.Name
  64.             };
  65.     }
  66.  
  67.     private static IEnumerable<EmployeeEntity> MapList2(List<object> o)
  68.     {
  69.         return
  70.             from si in o
  71.             let i = si as EmployeeDto
  72.             where i != null
  73.             select new EmployeeEntity
  74.             {
  75.                 Id = i.Id,
  76.                 FullName = i.Name
  77.             };
  78.     }
  79.  
  80. }
Success #stdin #stdout 1.35s 54696KB
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ElapsedTicks Solution 2 (let): 16115
https://ideone.com/0SP87
language:
C# (gmcs 5.20.1)
created:
12 years ago
visibility:
public

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