A minor problem my friend
Instead of
ShowApartments = dsGetGroups.Tables[0].Rows[Apartment]["ApartmentNumber"].ToString()
use,
ShowApartments += dsGetGroups.Tables[0].Rows[Apartment]["ApartmentNumber"].ToString()
Notice the =+ instead of =
Hope that helps. If it does mark it as solution and/or upvote.
Thanks
Milind