Troubles reloading section with more data in UITableView - ios

Question

I'm building an app which presents departures of busses. I use a tableview to represent it, the name of the busstop is set as the section header, and each row in a section represents a departure from that busstop.
The API always provide me with the next 20 departures for each stop, but initially I just show the next 6 departures in each section, I keep all the 20 in my datasource though. At the end of each section I have a cells which is supposed to double the shown departures in each section. It's done it this way:
tableView.beginUpdates()
tableView.reloadSections(NSIndexSet(index: indexPath.section) as IndexSet, with: .none)
tableView.endUpdates()
My initial thought was that I could just double the returnvalue of the numberOfRowsInSection-function for the specific section, but that doesn't seem to work.
var scale = [Int : Int]()
func numberOfSections(in tableView: UITableView) -> Int {
if stops.count != nil {
return stops.count
} else {
return 1
}
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return stops[indexPath.row].departures.count - scale[stops[section].id]
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
if stops != nil {
let currentDeparture = stops[(indexPath as NSIndexPath).section].departures![(indexPath as NSIndexPath).row]
let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as! DepartureTableViewCell
// Configuration of the cell
return cell
}
}
return UITableViewCell()
}
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
if indexPath.row == (stops[indexPath.row].departures.count)! {
var currentScale = scale[stops[indexPath.section].id]
scale[stops[indexPath.section].id] = currentScale - 6
tableView.beginUpdates()
tableView.reloadSections(NSIndexSet(index: indexPath.section) as IndexSet, with: .none)
tableView.endUpdates()
}
}
The dictionary scale is just mapping the ID of the stop to the number of departures that should be shown, starting at 14 (20-6) and each time the cell that is supposed to reload the section is tapped, it get reduced by 6. So we get 6 more departures in the given section. currentDepartureresInSection is the number of departures at the specific stop.
It is possible to do it this way, or do I have to update the datasource of the tableview?