c# - Linq Group By, Skip 1 where the skipped 1 was the most recent -

i have data set of objects have stored in events list (the variables have been declared earlier @ class level):

    [setup]     public void setup()     {         eventlogobj = new eventlogobj();          event1 = new eventlogobj() { recordid = 1, tablekey = "person_code=1", status = "s", eventtime = convert.todatetime("2013-07-15 14:00:00") };         event2 = new eventlogobj() { recordid = 2, tablekey = "person_code=2", status = "s", eventtime = convert.todatetime("2013-07-15 13:00:00") };         event3 = new eventlogobj() { recordid = 3, tablekey = "person_code=3", status = "s", eventtime = convert.todatetime("2013-07-15 13:00:00") };         event4 = new eventlogobj() { recordid = 4, tablekey = "person_code=2", status = "s", eventtime = convert.todatetime("2013-07-15 14:00:00") };         event5 = new eventlogobj() { recordid = 5, tablekey = "person_code=1", status = "s", eventtime = convert.todatetime("2013-07-15 13:00:00") };          events = new list<eventlogobj>() { event1, event2, event3, event4, event5 };     } 

i extracting duplicates - worked (below)

    [test]     public void storeonlyduplicatedetailsfromrowsintocollection()     {         var duplicates = events.groupby(s => s.tablekey)             .selectmany(grp => grp.skip(1)).tolist();          assert.areequal(2, duplicates.count);     } 

however, want extract duplicates lowest dates , i'm not quite sure how adjust linq query setup.

here have done far fails.

if wondering duplicates2 is, failed attempt implement this: linq: group aggregate still information recent row?

    [test]     public void pickduplicateeventwithleastdate()     {         var duplicates = events             //.orderby(e => e.eventtime)             .groupby(s => s.tablekey)             .selectmany(grp => grp.skip(1))             .tolist();          var duplicates2 = res in events                           group res res.tablekey g                           select new                           {                               count = g.count(),                               memberid = g.key,                               mostrecent = g.orderbydescending(x => x.eventtime)                               .first()                           };          assert.areequal(2, duplicates.count);         var e1 = duplicates[0];         var e2 = duplicates[1];          assert.areequal(e1.eventtime, convert.todatetime("2013-07-15 13:00:00"));         assert.areequal(e2.eventtime, convert.todatetime("2013-07-15 13:00:00"));     } 

if want try without having setup interfaces, classes, etc in visual studio, see here https://dotnetfiddle.net/yyosfm , fiddle about. if tests pass, should nothing in 'console window'.

you skipping first item, must 1 highest date. achieve this, need use orderbydescending belongs inside selectmany before skip.

 var duplicates = events             .groupby(s => s.tablekey)             .selectmany(grp => grp.orderbydescending(e => e.eventtime)                                   .skip(1))             .tolist(); 

if want remaining duplicates ordered ascending, add .orderby(e => e.eventtime) right after skip.

oh, , test data bogus. first data item person_code=1 2013-07-13 should on 2013-07-15 pass test suite.