一个Linq Group By 和Sum的范例

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转自:http://www.cnblogs.com/sskset/archive/2012/09/06/2674055.html

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.IO;namespace ConsoleApplication3{    class Program    {        static void Main(string[] args)        {            var Items = new List<SortItem>();            Items.AddRange(new SortItem[] {                 new SortItem(){ GroupId = 1, Id=1, Count = 1, Weight = 100 },                new SortItem(){ GroupId = 1, Id=1, Count = 2, Weight = null },                new SortItem(){ GroupId = 1, Id =2, Count = 3, Weight = 300 },                new SortItem(){ GroupId = 2, Id=1, Count = 2, Weight = 200 },                new SortItem(){ GroupId = 2, Id=2, Count = 2, Weight = 200 },                new SortItem(){ GroupId = 2, Id=3, Count = 4, Weight = null },                new SortItem(){ GroupId = 3, Id=3 ,Count = 2, Weight = null },                new SortItem(){ GroupId = 1, Id =2, Count = 6, Weight = 300 },            });            var data = (from a in Items                        group a by new { a.GroupId, a.Id } into b                        orderby new ComparerItem() { GroupId = b.Key.GroupId, Id = b.Key.Id } descending                        select new                        {                            GroupId = b.Key.GroupId,                            Id = b.Key.Id,                            Count = b.Sum(c => c.Count),                            Weight = b.Sum(c => c.Weight)                        }).OrderBy(t => t.GroupId).ThenBy(t => t.Id);            foreach (var anItem in data)                Console.WriteLine("GroupId:{0} Id:{1} Count:{2} Weight:{3}", anItem.GroupId, anItem.Id, anItem.Count, anItem.Weight);            Console.ReadKey();        }        class ComparerItem : IComparable        {            public int GroupId { get; set; }            public int Id { get; set; }            public int CompareTo(object obj)            {                var tem = (ComparerItem)obj;                if (this.GroupId == tem.GroupId)                {                    if (this.Id > tem.Id) return 1;                    else if (this.Id < tem.Id) return -1;                    return 0;                }                else if (this.GroupId > tem.GroupId)                {                    return 1;                }                return -1;            }        }        class SortItem        {            public int GroupId { get; set; }            public int Id { get; set; }            public int Count { get; set; }            public int? Weight { get; set; }        }    }}

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