Java Stream. Extracting distinct values of multiple maps

Question

I am trying to extract and count the number of different elements in the values of a map. The thing is that it's not just a map, but many of them and they're to be obtained from a list of maps.

Specifically, I have a Tournament class with a List<Event> event member. An event has a Map<Localization, Set<Timeslot>> unavailableLocalizations member. I would like to count the distincts for all those timeslots values.

So far I managed to count the distincts in just one map like this:

event.getUnavailableLocalizations().values().stream().distinct().count()

But what I can't figure out is how to do that for all the maps instead of for just one.

I guess I would need some way to take each event's map's values and put all that into the stream, then the rest would be just as I did.

Answer 1

Let's do it step by step:

listOfEvents.stream() //stream the events
            .map(Event::getUnavailableLocalizations) //for each event, get the map
            .map(Map::values) //get the values
            .flatMap(Collection::stream) //flatMap to merge all the values into one stream
            .distinct() //remove duplicates
            .count();   //count