How to preserve informations about original observable on RxJava2 - rx-java2

Question

I have a REST call returning a collection (the original), this collection is filtered but on the subscribe onSuccess I what to obtain both the original list and the filtered one.
I don't know how to 'pass' this second element, which operator should I use to obtain this result?
I show a simplified version of my code below
Observable.fromCallable(new Callable<List<Integer>>() {
#Override public List<Integer> call() throws Exception {
// dynamic list obtained from REST call
// for simplicity here I return a list
return Arrays.asList(1, 2, 3, 4);
}
})
.flatMap(new Function<List<Integer>, ObservableSource<Integer>>() {
#Override public ObservableSource<Integer> apply(List<Integer> integers) throws Exception {
return Observable.fromIterable(integers);
}
})
.filter(new Predicate<Integer>() {
#Override public boolean test(Integer integer) throws Exception {
return integer > 2;
}
})
.toList()
.subscribe(new SingleObserver<List<Integer>>() {
#Override public void onSubscribe(Disposable d) {}
#Override public void onSuccess(List<Integer> value) {
///////////////////
// here I want both original and filtered list
///////////////////
}
#Override public void onError(Throwable e) {}
});

Answer 1

One way is with ConnectableObservable. You need to share the emissions of your initial stream. Something like this
ConnectableObservable<List<Integer>> connectableObservable
= Observable.fromCallable(() -> {
// dynamic list obtained from REST call
// for simplicity here I return a list
return Arrays.asList(1, 2, 3, 4);
}).publish();
Single.zip(connectableObservable.flatMapIterable(integers -> integers)
.filter(integer -> integer > 2)
.toList(),
connectableObservable.elementAtOrError(0),
(integers, lists) -> combine(integers, lists))
.subscribe(o -> {
///////////////////
// here you ll have a new object containing both the initial list and the filtered list
///////////////////
});
connectableObservable.connect();