Unique values only (Firebase)

Hello, we are building an app with a lots of routes (Departure airport ->Arrival Airport) We currently have all the data in one collection called Routes and each document has a departure and an arrival airport. We are trying to firstly display all the departure airport to the user, but since there are 50 routes with departure airport Vienna, it displays Vienna 50 times. Can anyone suggest how to display each airport only once?

Thank you in advance. :slight_smile:

In the “forumula functions” there is UNIQUE_BY_KEY ; to me it looks like it can do what you are looking for.