rxAndroidExample.java

interface PlacesService {
    @GET("places/{id}")
    Observable<Place> getPlaceById(@Path("id") int placeId);
}

interface UsersService {
    @GET("users")
    Observable<List<User>> listUsers();
}

class Datasource {
    public void getUsersWithPlace() {
        userService.listUsers()
                .flatMapIterable(users -> users)
                .flatMap(user -> placesService.getPlaceById(user.placeId),
                        (user, place) -> user.name + " - " + place.title)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Observer<String>() {
                    ArrayList<String> dataSet = new ArrayList<String>();
                    @Override
                    public void onSubscribe(Disposable d) {
                        disposables.add(d);
                    }

                    @Override
                    public void onNext(String s) {
                        dataSet.add(s);
                    }

                    @Override
                    public void onError(Throwable e) {
                        Log.e(TAG, "onError: ",e );
                    }

                    @Override
                    public void onComplete() {
                        for (Disposable disposable : disposables ) {
                            if (!disposable.isDisposed()){
                                disposable.dispose();
                            }
                        }
                        updateAdapter(dataSet.toArray(new String[0]));
                    }
                });
    }
}