RX Transformers

rx-transformers-incremement.java

public static Observable.Transformer<Integer, Integer> increment() {
  return new Observable.Transformer<Integer, Integer>() {
    private Integer previous = 0;

    @Override
    public Observable<Integer> call(Observable<Integer> integerObservable) {
      return integerObservable.map(i -> {
        Integer val = i + previous;
        previous = val;
        return val;
      });
    }
  };
}

Observable.from(new Integer[]{1,2,3}).compose(incremenent()).subscribe(i->Log.d("Number: ",i))
//outputs 1,3,6