RxJava - Any way to combine scanning and flatMap?

Question

Say I have a function that accepts Stringand longand returns a Single<String>.

Single<String> stringAddition(String someString, long value) {
  return Single.just(someString + Long.toString(value));
}

Now i have this Observable...

Observable.interval(1, SECONDS)
  .scan("", (cumulativeString, item) -> {
    // Need to return the result of stringAddition(cummulativeString, item)
  });

I don’t understand how to do this. Scanning requires me to return String, but I would like to use a method that returns Single<String>. It seems to me that I need something that can combine behavior, both scan, and flatMap. Is there any RxJava2 magic that can help me?

Answer 1

. , stringAddition Observable

Observable<String> scanned = Observable.interval(1, TimeUnit.SECONDS)
            .scan(
                    Observable.just(""),
                    (cumulativeString, item) ->
                        cumulativeString
                          .flatMap(str -> stringAddition(str, item).toObservable())
            )
            .flatMap(it -> it);