LINQ查询以获取分组表中具有最大日期的行

Question

I have following datatable structure

ID    Date            Vendor  Grade
 1    20-nov-2013     xyz      A
 2    26-Apr-2013     abc      B
 1    21-nov-2013     pqr      D
 1    10-nov-2013     abc      C
 2    15-dec-2013     pqr      A
 2    20-May-2013     abc      B

What i want group this table on column ID and then select the row that has maximum dateTime value

Sample Answer would be for this table is

ID    Date            Vendor  Grade
 1    21-nov-2013     pqr      D
 2    15-dec-2013     pqr      A

I have tried following so far but struck with no clue what to do next

var chk = (from s in dt.AsEnumerable()
          where s.Field<int>("ID") == 1 || s.Field<int>("ID") == 2            
          select s).GroupBy(k => k.Field<int>("ID")});

Answer 1

Group your rows by ID , then sort each group of rows by Date and select first one row:

var chk = from r in dt.AsEnumerable()
          let id = r.Field<int>("ID")
          where id == 1 || id == 2
          group r by id into g
          select g.OrderByDescending(r => r.Field<DateTime>("Date")).First();

Produces

ID    Date            Vendor  Grade
 1    21-nov-2013     pqr      D
 2    15-dec-2013     pqr      A

Answer 2

Query syntax:

  var chk = from r in dt.AsEnumerable() /*where 1=1 */
                  group r by r.Field<int>("ID") into g
                  select g.OrderByDescending(t => t.Field<int>("ID")).First();

Fluent syntax :

 dt.AsEnumerable().GroupBy(r => r.Field<int>("ID")).Select(g => g.OrderByDescending(t => t.Field<int>("ID")).First());