Attempt to implement headAndTail function. Using publish().refCount() to avoid double reading a file. Doesn't work at all.

HeadTest.java

public class HeadTest {
    public static void main(String[] args) {
        Observable<Integer> fileReader = Observable.create((Observable.OnSubscribe<Integer>) subscriber -> {
            System.out.println("Reading from a file");
            subscriber.onNext(100);  // header

            for (int i = 0; i < 10; ++i) {
                subscriber.onNext(i);
            }

            subscriber.onCompleted();
        });

        Pair<Observable<Integer>, Observable<Integer>> headAndTail = headAndTail(fileReader);

        Integer headerValue = BlockingObservable.from(headAndTail.x).single();
        Observable<Integer> processedValues = headAndTail.y.map(i -> i + headerValue);

        BlockingObservable.from(processedValues).forEach(System.out::println);
    }

    public static <T> Pair<Observable<T>, Observable<T>> headAndTail(Observable<T> o) {
        Observable<T> published = o.publish().refCount();
        return new Pair<>(published.first(), published.skip(1));
    }

    public static class Pair<X, Y> {
        public final X x;
        public final Y y;

        public Pair(X x, Y y) {
            this.x = x;
            this.y = y;
        }
    }
}

output

Reading from a file