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  1. using System;
  2. using System.Linq;
  3. using System.Collections.Generic;
  4.  
  5. class M
  6. {
  7.     class Student { public int Id { get; set; } public string Name { get; set; } public char Order { get; set; } }
  8.     class Class { public int Id { get; set; } public string Title { get; set; } }
  9.     class SickDay { public int Id { get; set; } public int StudentId { get; set; } public int ClassId { get; set; } }
  10.  
  11.     static void Main(string[] args)
  12. {
  13.     var Students = new List<Student>()
  14.     {
  15.         new Student { Id = 1, Name = "Al", Order = 'a' },
  16.         new Student { Id = 2, Name = "Betty", Order = 'b' },
  17.         new Student { Id = 3, Name = "Charles", Order = 'c' },
  18.     };
  19.  
  20.     var Classes = new List<Class>()
  21. {
  22. new Class { Id = 1, Title = "A100" },
  23. new Class { Id = 2, Title = "A200" },
  24. };
  25.  
  26. var SickDays = new List<SickDay>()
  27. {
  28. new SickDay { Id = 1, StudentId = 1, ClassId = 2 },
  29. new SickDay { Id = 2, StudentId = 1, ClassId = 2 },
  30. new SickDay { Id = 3, StudentId = 1, ClassId = 2 },
  31. new SickDay { Id = 4, StudentId = 1, ClassId = 2 },
  32. new SickDay { Id = 5, StudentId = 2, ClassId = 1 },
  33. };
  34.  
  35. var myId = 2;
  36.  
  37. var query =
  38.     from s in Students
  39.     join d in SickDays on s.Id equals d.StudentId into gj
  40.     from sd in gj.DefaultIfEmpty()
  41.     group sd by new { s.Name, s.Order } into gg
  42.     select
  43.         new
  44.         {
  45.             Name = gg.Key.Name,
  46.             Order = gg.Key.Order,
  47.             Count = gg.Count(x => x != null && x.ClassId == myId)
  48.         };
  49. foreach (var q in query)
  50. {
  51. Console.WriteLine("{0}\t{1}\t{2}", q.Name, q.Order, q.Count);
  52. }
  53. }
  54. }
Success #stdin #stdout 0.06s 37424KB
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stdin
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Standard input is empty
stdout
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Al	a	4
Betty	b	0
Charles	c	0
https://ideone.com/p12ts
language:
C# (gmcs 5.20.1)
created:
11 years ago
visibility:
public

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