To remove duplicates and not repeat the same item

clear row.Item;
 itm_list = List();
 rem_list = List();
 fet_cat = Expense_Item[Expense_Categories == input.Category].ID.getAll();
 itm_list.addAll(fet_cat);
 for each val in input.Item
 {
  if(val.Item != null)
  {
 	 rem_list.add(val.Item);
  }
 }
  if(itm_list.size() > 0 && rem_list.size() > 0)
  {
   itm_list.removeAll(rem_list);
   row.Item:ui.add(itm_list);
  }
  else
  {
  row.Item:ui.add(itm_list);
  }