Try it

Observable.just(new ArrayList<String>())
				.flatMap(new Func1<ArrayList<String>, Observable<String>>() {
					@Override
					public Observable<String> call(ArrayList<String> strings) {
						int N = 10;
						return Observable.range(0, strings.size() / N)
								.flatMap(count -> {
									return Observable.from(strings)
											.skip(count * N)
											.take(count * N)
											.toList();
								});
					}
				});