Question

If i have table something like:

col1         col2    col3   col4
apple        1        35    1    
apple        1        38    0    
apple        2        27    1    
orange       1        50    0    
orange       2        51    1    

I want to group by 1 an 2 column, and max col3. at the end i want get:

apple        1        38    0  
apple        2        27    1    
orange       1        50    0 
orange       2        51    1  

what is linq query to this?

Answer 1

Second attempt.

var subquery = 
(from r in table group r by new { r.col1, r.col2} into results
   select new 
   { 
      results.Key.col1, 
      results.Key.col2, 
       MaxCol3 = results.Max(i=>i.col3)
   }
  ) ;


var query2 = 
    (from r in subquery1 
       select new 
       { 
       r.col1 , 
       r.col2 , 
       r.MaxCol3 , 
       col4 = (from x in subquery1 
            where r.col1 == x.col1 && r.col2 == x.col2 && x.col3 == r.MaxCol3 
            select x.col4).First()
       }
   );  

I have never used this syntax, but I think you can also do something like.

 (from r in table group r by new { r.col1, r.col2} into results
   let MaxCol3 = results.Max(i=>i.col3)
   select new 
    { 
      results.Key.col1, 
      results.Key.col2, 
       MaxCol3 ,
      col4 = results.First(i=>i.col3 == MaxCol3).col4
    }
  ) ;