RxJava flatMapIterable with a Single

You can convert Single to Observable by using operator toObservable()

It will look like this:

getListOfItems()
    .toObservable()
    .flatMapIterable(items -> items)
    .flatMap(item -> doSomethingWithItem())
    .toList()

Building on the answer from yosriz, this is what I ended up with in Kotlin

getListOfItems()
        .flattenAsObservable { it }
        .flatMap { doSomethingWithItem(it) }
        .toList()

The same can be achieved using Kotlin's map, depending on your preference:

getListOfItems()
        .map { items ->
            items.map {
                doSomethingWithItem(it)
            }
        }

flattenAsObservable should do the trick, it will map Single success value to Iterable (list), and emit each item of the list as an Observable.

  getListOfItems()
            .flattenAsObservable(new Function<Object, Iterable<?>>() {
                @Override
                public Iterable<?> apply(@NonNull Object o) throws Exception {
                    return toItems(o);
                }
            })
            .flatMap(item -> doSomethingWithItem())
            .toList()