如何从Observable <list <type>＆gt;创建一个Observable <type>

Question

如果我有Observable List个Letter

public Observable<List<Letter>> getAToZList() {
        return Observable.create(
                new Observable.OnSubscribe<List<Letter>>() {
                    @Override
                    public void call(Subscriber<? super List<Letter>> subscriber) {
                        List<Letter> aToZLetters = getLetters();
                        subscriber.onNext(aToZLetters);
                        subscriber.onCompleted();
                    }
                }
        );
    }

如何创建一个观察单Observable的{​​{1}}，并在Letter中为每个List发一个？{/ p>

public Observable<Letter> getAToZ() {
        return Observable.create(
                     getAToZList().something() ??
        );
    }

https://github.com/ReactiveX/RxJava