c# - List is empty after linq operation -

i have problem understend happening in foreach loop- listofbookedtimes successfuly gets elements want, after execution of next line listofbookedtimes empty. why? (all lists contain datetime)

  foreach (var day in alldays)         {             list = rep.getlistofworkinghours(fulldayworkinghours, day, spworkinghours);             bookedtimes = _bookingsservice.getbookedtimes(day, providerid);             foreach (var b in bookedtimes)             {                 var listofbookedtimes = list.where(m => m.timeofday == (b.timeofappointment.timeofday));                 list.removeall(m => m.timeofday == (b.timeofappointment.timeofday));                 listofbookedtimes.select(m => m.year - 50);                 list.addrange(listofbookedtimes);              } 

your problem not removeall rather fundemental understanding of linq , yield return.

when call

list.where(m => m.timeofday == (b.timeofappointment.timeofday)); 

it not executed rather returns enumerator filter collection on iteration. in next line remove entries wanted fetch in previous line.

when iterate collection in

list.addrange(listofbookedtimes); 

it empty.

solution: add .toarray() or .tolist() after where , should work expected. this:

var listofbookeditems = list.where(m => m.timeofday == (b.timeofappointment.timeofday))                             .tolist();