public static <T, U> Collector<T, ?, Optional<Long>> rankBy(U value, Function<? super T, ? extends U> function, Comparator<? super U> comparator) {
        return Collector.of(
            () -> new long[] { -1L },
            (l, v) -> {
                if (l[0] == -1L)
                    l[0] = 0L;

                if (comparator.compare(value, function.apply(v)) > 0)
                    l[0] = l[0] + 1L;
            },
            (l1, l2) -> {
                l1[0] = (l1[0] == -1 ? 0L : l1[0]) +
                        (l2[0] == -1 ? 0L : l2[0]);

                return l1;
            },
            l -> l[0] == -1 ? Optional.empty() : Optional.of((long) l[0])
        );
    }
Get a {@link Collector} that calculates the derived <code>RANK()</code> function given a specific ordering.
jOOL-java-8/src/main/java/org/jooq/lambda/Agg.java