一个Linq Group By 和Sum的范例

1 using System;
2 using System.Collections.Generic;
3 using System.Linq;
4 using System.Text;
5 using System.IO;
6
7 namespace ConsoleApplication3
8 {
9     class Program
10     {
11         static void Main(string[] args)
12         {
13             var Items = new List<SortItem>();
14
15             Items.AddRange(new SortItem[] {
16                 new SortItem(){ GroupId = 1, Id=1, Count = 1, Weight = 100 },
17                 new SortItem(){ GroupId = 1, Id=1, Count = 2, Weight = null },
18                 new SortItem(){ GroupId = 1, Id =2, Count = 3, Weight = 300 },
19                 new SortItem(){ GroupId = 2, Id=1, Count = 2, Weight = 200 },
20                 new SortItem(){ GroupId = 2, Id=2, Count = 2, Weight = 200 },
21                 new SortItem(){ GroupId = 2, Id=3, Count = 4, Weight = null },
22                 new SortItem(){ GroupId = 3, Id=3 ,Count = 2, Weight = null },
23                 new SortItem(){ GroupId = 1, Id =2, Count = 6, Weight = 300 },
24             });
25
26             var data = (from a in Items
27                         group a by new { a.GroupId, a.Id } into b
28                         orderby new ComparerItem() { GroupId = b.Key.GroupId, Id = b.Key.Id } descending
29                         select new
30                         {
31                             GroupId = b.Key.GroupId,
32                             Id = b.Key.Id,
33                             Count = b.Sum(c => c.Count),
34                             Weight = b.Sum(c => c.Weight)
35                         }).OrderBy(t => t.GroupId).ThenBy(t => t.Id);
36
37
38             foreach (var anItem in data)
39                 Console.WriteLine("GroupId:{0} Id:{1} Count:{2} Weight:{3}", anItem.GroupId, anItem.Id, anItem.Count, anItem.Weight);
40
41             Console.ReadKey();
42         }
43
44         class ComparerItem : IComparable
45         {
46             public int GroupId { get; set; }
47             public int Id { get; set; }
48
49             public int CompareTo(object obj)
50             {
51                 var tem = (ComparerItem)obj;
52
53                 if (this.GroupId == tem.GroupId)
54                 {
55                     if (this.Id > tem.Id) return 1;
56                     else if (this.Id < tem.Id) return -1;
57
58                     return 0;
59                 }
60                 else if (this.GroupId > tem.GroupId)
61                 {
62                     return 1;
63                 }
64
65                 return -1;
66             }
67         }
68
69
70         class SortItem
71         {
72             public int GroupId { get; set; }
73             public int Id { get; set; }
74             public int Count { get; set; }
75             public int? Weight { get; set; }
76         }
77     }
78 }