I have one observable with a list of String and another with a list of string lists.
I need to reuse first observable until every string is stetted

In short. I need to iterate through every element of the list's list and attach it to first observable list elements

I learned about retryWhen but don't know how to reuse first observable and continue on the second

```
val cat = sheetsViewer.GOOGLE_SHEETS_ENDPOINT_IMPL.readSpreadSheet(spreadsheetId, "A4:DA4")
            .toObservable()
            .flatMap { Observable.fromIterable(it) }

val data = sheetsViewer.GOOGLE_SHEETS_ENDPOINT_IMPL.readSpreadSheet(spreadsheetId, range)
            .toObservable()
            .subscribeOn(Schedulers.computation())
            .flatMap { Observable.fromIterable(it) }
            .map {
                val newList = it.toMutableList()

                while (newList.size != 105)
                    newList.add("")

                return@map newList
            }

```

I have list of strings {"a", "b"}
and second {{"a", "b"}, {"c", "d"}, {"e", "f"}}

I expect the output to be {"aa", "bb", "ca", "db", "ea", "fb"}