linq group by having 实现

TO XML ，优化的重点还是在细节，细节决定成败一点也没错

 

 

 
  
        System.Diagnostics.Stopwatch st1 =  
   new System.Diagnostics.Stopwatch(); 
   
            st1.Start(); 
   
            XDocument xdom = XDocument.Load(XmlPath); 
   
             
   var restElements = xdom.Descendants( 
   " 
   rest 
   ").ToList(); 
   
            st1.Stop(); 
   
            HttpContext.Current.Response.Write( 
   " 
   1.载入XML时间 
   " + st1.ElapsedMilliseconds +  
   " 
   <br> 
   "); 
   
 

 

载入一个大一点的文件，我这里显示花时间 1700毫秒 左右

 

 

 
  
               System.Diagnostics.Stopwatch st =  
   new System.Diagnostics.Stopwatch(); 
   
            st.Start(); 
   
             
   var Hotels = ( 
   from hotels  
   in restElements 
   
                           
   where   
   
  
                              hotels.Element( 
   " 
   lat 
   ") !=  
   null &&   
   
  
                              hotels.Element( 
   " 
   lat 
   ").Value !=  
   string.Empty  
   
                           
   select  
   new 
   
                          { 
   
                              State = hotels.Element( 
   " 
   state 
   ").Value, 
   
                              StateCityKey = (hotels.Element( 
   " 
   state 
   ").Value +  
   " 
   - 
   " + hotels.Element( 
   " 
   city 
   ").Value).ToUpper() 
   
                          }).ToList(); 
   
 

 

过滤，，生成匿名对象，然后Tolist();这一步的没什么好说的，关键是不要让他监视XML文件，不要让他延时加载，生成一个KEY

 

 
  
                 
   var hotelsGroup = 
   
                ( 
   from hotel  
   in Hotels 
   
                 group hotel by hotel.StateCityKey 
   
                     into h 
   
                      
   select  
   new 
   
                     { 
   
                         StateCityKey = h.Key, 
   
                         count = h.Count(), 
   
                         hgrou = h 
   
                     } into c 
   
                      
   where c.count >  
   2 
   
                      
   select c).ToList(); 
   
            st.Stop(); 
   
            HttpContext.Current.Response.Write( 
   " 
   2.分组耗费 
   " + st.ElapsedMilliseconds); 
   
             
   long a = st1.ElapsedMilliseconds + st.ElapsedMilliseconds; 
   
            HttpContext.Current.Response.Write( 
   " 
   <br>1+2总耗费 ： 
   " + a +  
   " 
   毫秒<br> 
   "); 
   
 

 

 分组耗时：40毫秒

通过KEY（StateCityKey）进行分组，注意COUNT，where c.count > 2 对分组以后的数据进行判断，相当于HAVING

用的不是COUNT（） 是count  ，

 

下面的循环统计输出就不放出来了。。。

 

 转载请放链接 http://www.cnblogs.com/jacd/archive/2012/04/25/2469389.html