How to execute 2 requests sequentially in RxJava2?

Question

Android

There are 2 different services. The first one returns a list of cities, for the second request we pass the id of the city and get the weather.
The output is a list of cities with the weather for today.

Answer 1

On kotlin like this:

requestCityList()
    .switchMap { cityList -> 
        cityList.map { city -> requestWeather(city.id) }.combineLatest { it }
    }

In the Java version, Observable.combineLatest(Iterable, Function) is used similarly.