linq group by having 實現

TO XML ，優化的重點還是在細節，細節決定成敗一點也沒錯

 

 

 
          
                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.載入XML時間 
           " + st1.ElapsedMilliseconds +  
           " 
           <br> 
           "); 
           
         

 

載入一個大一點的文件，我這里顯示花時間 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(); 
           
         

 

過濾，，生成匿名對象，然后Tolist();這一步的沒什么好說的，關鍵是不要讓他監視XML文件，不要讓他延時加載，生成一個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.分組耗費 
           " + st.ElapsedMilliseconds); 
           
             
           long a = st1.ElapsedMilliseconds + st.ElapsedMilliseconds; 
           
            HttpContext.Current.Response.Write( 
           " 
           <br>1+2總耗費 ： 
           " + a +  
           " 
           毫秒<br> 
           "); 
           
         

 

 分組耗時：40毫秒

通過KEY（StateCityKey）進行分組，注意COUNT，where c.count > 2 對分組以后的數據進行判斷，相當於HAVING

用的不是COUNT（） 是count  ，

 

下面的循環統計輸出就不放出來了。。。

 

 轉載請放鏈接 http://www.cnblogs.com/jacd/archive/2012/04/25/2469389.html