@SuppressWarnings("unchecked")
@Override
default <C> Map<C, Seq<T>> groupBy(Function<? super T, ? extends C> classifier) {
Objects.requireNonNull(classifier, "classifier is null");
if (isEmpty()) {
return HashMap.empty();
} else {
return (Map<C, Seq<T>>) traverse().groupBy(classifier);
}
}
@Override
public <C> Map<C, Array<T>> groupBy(Function<? super T, ? extends C> classifier) {
return foldLeft(
HashMap.empty(),
(map, t) -> {
final C key = classifier.apply(t);
final Array<T> values = map.get(key).map(ts -> ts.append(t)).getOrElse(of(t));
return map.put(key, values);
});
}