c# - Get latest record and group with highest date - LINQ -

i have table billing below

accoundid | group | dateofbill 1234      |     | 2017-07-12 1234      | b     | 2017-07-16 1234      | c     | 2017-07-31 1235      |     | 2017-07-31 1236      | b     | 2017-07-31 

as see, accountid 1234 have made 3 transaction on july 2017. need list accountid 1234 must in group c because that's latest date on transaction.

here code snippet

var latestaccount = n in billing                     (n.group == "a" || n.group == "b" || n.group == "c")                     group n new { n.accountid, n.group } g                     select new {                          accountid = g.key.accountid,                          group = g.key.group ,                          dateofbill = g.max(t => t.dateofbill)                      }; 

but result wrong. how in linq?

class program {     static void main(string[] args)     {         list<billing> billings = new list<billing>()         {             new billing()             {                 accountid = 1234, dateofbill = new datetime(2017,07,12), group = "a"              },             new billing()             {                 accountid = 1234, dateofbill = new datetime(2017,07,16), group = "b"              },             new billing()             {                 accountid = 1234, dateofbill = new datetime(2017,07,31), group = "c"              },             new billing()             {                 accountid = 1235, dateofbill = new datetime(2017,07,31), group = "a"              },             new billing()             {                 accountid = 1236, dateofbill = new datetime(2017,07,31), group = "b"              }                        };          var latestaccount = n in billings                             (n.group == "a" || n.group == "b" || n.group == "c")                             group n new { n.accountid } g                             select g.where(d => d.dateofbill == g.max(m => m.dateofbill)).select(x => new { accountid = g.key.accountid, group = x.group, dateofbill = x.dateofbill }).firstordefault();          foreach (var item in latestaccount)         {             console.writeline("accountid: " + item.accountid + "  date of bill: " + item.dateofbill + "  group: "+ item.group);         }         console.readline();     } } class  billing {     public int accountid { get; set; }     public string group { get; set; }     public datetime dateofbill { get; set; } } 

is below want? if show me output want, can modify answer.