LinQ转换运算符ToLookup

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ToLookupDemo
{
    class Program
    {
        //自定义类
        public class Product
        {
            public string Code { get; set; }
            public string Description { get; set; }
        }
        static void Main(string[] args)
        {
            List<Product> products = new List<Product>
            {
                new Product{Code="SPM1",Description="1"},
                new Product{Code="LME1",Description="3"},
                new Product{Code="SUP1",Description="4"},
                new Product{Code="SPM2",Description="2"},
                new Product{Code="SUP2",Description="5"}
            };
            //转换为Lookup类型，得到的结果已经分组了
            Lookup<string, string> lookup = (Lookup<string, string>)
                products.ToLookup(c => c.Code.Substring(0, 3), c => c.Code + " " + c.Description);
            //在结果中循环
            foreach (IGrouping<string, string> group in lookup)
            {
                Console.WriteLine(group.Key);
                foreach (string s in group)
                    Console.WriteLine("   {0}", s);
            }
            Console.ReadLine();
            //取得其中一组值
            IEnumerable<string> spmGroup = lookup["SPM"];
            foreach (var str in spmGroup)
                Console.WriteLine(str);
            Console.ReadLine();
        }
    }
}