Collection<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5); Observable.from(numbers) .filter(number -> number % 2 == 0) .subscribe(System.out::println); Collection<Integer> numbers1 = Arrays.asList(1, 2, 3); Collection<Integer> numbers2 = Arrays.asList(4, 5, 6); Observable<Integer> merged = Observable.merge( Observable.from(numbers1), Observable.from(numbers2) ); merged.subscribe(System.out::println); Observable.from(someDataSource) .map(data -> convertToEntity(data)) .subscribe( );