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  1. using System;
  2. using System.Collections.Generic;
  3. using System.Linq;
  4.  
  5. namespace Teratail47399
  6. {
  7.     class Program
  8.     {
  9.         class SampleTable
  10.         {
  11.             public long Id;
  12.             public string User;
  13.             public DateTime LoginDate;
  14.         }
  15.  
  16.         static void Main(string[] args)
  17.         {
  18.             var list = new List<SampleTable>();
  19.  
  20.             list.Add(new SampleTable()
  21.             {
  22.                 Id = 0,
  23.                 User = "user01",
  24.                 LoginDate = DateTime.Parse("2016/08/09 13:00")
  25.             });
  26.  
  27.             list.Add(new SampleTable()
  28.             {
  29.                 Id = 1,
  30.                 User = "user01",
  31.                 LoginDate = DateTime.Parse("2016/09/09 13:00")
  32.             });
  33.  
  34.             list.Add(new SampleTable()
  35.             {
  36.                 Id = 2,
  37.                 User = "user01",
  38.                 LoginDate = DateTime.Parse("2016/09/10 13:00")
  39.             });
  40.  
  41.             list.Add(new SampleTable()
  42.             {
  43.                 Id = 3,
  44.                 User = "user02",
  45.                 LoginDate = DateTime.Parse("2016/09/10 13:00")
  46.             });
  47.  
  48.             foreach (var data in list.Where(x => x.User == "user01").GroupBy(x => x.LoginDate.ToString("yyyy/MM")))
  49.             {
  50.                 Console.WriteLine($"{data.Key} {data.Count()}回");
  51.             }
  52.         }
  53.     }
  54. }
Success #stdin #stdout 0.02s 30072KB
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2016/08 1回
2016/09 2回
https://ideone.com/couziu
language:
C# (gmcs 5.20.1)
created:
9 years ago
visibility:
public

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