static <T, K> Map<K, List<T>> groupBy(Stream<? extends T> stream, Function<? super T, ? extends K> classifier) {
        return Seq.<T>seq(stream).groupBy(classifier);
    }
Shortcut for calling {@link Stream#collect(Collector)} with a
{@link Collectors#groupingBy(Function)} collector.
jOOL/src/main/java/org/jooq/lambda/Seq.java