LinQ对一个大的List根据其中对象的属性进行分组为小的List

var res=from m in masterList where m.level>8 &&m.menpai=="丐帮"select  m;(表达式的写法)
var res=from m in masterList where m.level>8 select  m.name;
foreach(var temp in res)
{
cw(temp)
}

var res= masterList.Where(Test);//list中的每个元素都会调用where

　1.联合查询

var res= from m in masterList 
             from k in kongfuList 
             where m.kongfu==k.name&&k.Power>90//先联合后限制
              select  new(master=m,kongfu=k);//创建了两个临时对象  做映射
            select m;//所学功夫杀伤力>90的武林高手
扩展方法的用法：
var res=masterList.selectMany(m=>kongfuList,(m,k)=>new{master=m,kongfu=k});//做映射

var res=masterList.selectMany(m=>kongfuList,(m,k)=>new{master=m,kongfu=k}).where(x=>x.master.kongfu==x.kongfu.name&&x.kongfu.Power>90);//

　　2.排序

var res=from m in masterList//设置查询的集合
            where m.level>8&&m.menpai="丐帮"//通过&&添加并列的条件
          orderby m.Age  m.level descending（或者m.level)//按照多个字段排序
            select m;//表示m的结果结合返回    

扩展方法：
var res=masterList.Where(m=>m.level>8&&m.menpai=="丐帮").Orderby(m=>m.Age);
var res=masterList.Where(m=>m.level>8&&m.menpai=="丐帮").Orderby(m=>m.Age).Thenby(m=>m.age);

　　3.join on 集合联合

var res=from m in maseterList
            join k in kongfuList on m.kongfu equals k.Name
           where k.Power>90
            select new {master=m,kongfu=k};//    

　　4.分组查询（把武林高手按照所学功夫分类）

var res-from k in kongfuList
            join m in masterList on k.name equals m.kongfu
            into groups
            orderby groups.Count()
            select new{kongfu=k,count=groups.count()};

　　5.按照自身字段分组group

var res=from m in masterList
            group m by menpai into g
            select new {count=g.count(),g.key}//g.key,key表示按照哪个属性分的组

　　6.量词操作

bool res=masterList.Any(m=>m.menpai=="长流");
bool res=masterList.All(m=>m.menpai="长流");

 实践操作：项目中遇到一个问题，需要把一个大的list，根据其中对象的属性再次进行拆分成多个小的list操作如下

 public  class FeatWithBSM
    {
        public IFeature feature { get; set; }
        public string BSM { get; set; }
     }
 public  class FeatureCate
    {
       public List<FeatWithBSM> features;
       public string BSM;
       public double SumArea;

       public string  ZDGN_1;
       public string ZYSZ_1;
       public string LZ_1;
       public string ZXJL_1;
　　}

List<FeatWithBSM> featureList= searchFeatures("",layer);//初始化最大的原始的List
             var group1 = featureList.GroupBy(x => x.BSM).Select(x => 
                 new FeatureCate {
                     BSM = x.Key, features = x.ToList() 
                 }).ToList();

　在GroupBy中的参数x是list中的单个FeatWithBSM,返回值是IEnumerable<IGroup<string,FeatWithBSM>>

　在Select中的参数x是IGroup<string,FeatWithBSM> 箭头函数输出的是新的类的实例 FeatureCate