Transformers.java

public class Transformers {

    public static <T> Observable.Transformer<Iterable<T>, T> flatten()  {
        return new Observable.Transformer<Iterable<T>, T>() {
            @Override
            public Observable<T> call(Observable<Iterable<T>> iterableObservable) {
                return iterableObservable.flatMap(new Func1<Iterable<T>, Observable<T>>() {
                    @Override
                    public Observable<T> call(Iterable<T> iterable) {
                        return Observable.from(iterable);
                    }
                });
            }
        };
    }
}