public static <T> Aggregator<T, Vector, ?> valueCounts() {
return Aggregator.of(
() -> new HashMap<T, Integer>(),
(map, t) -> map.compute(t, (v, c) -> c == null ? 1 : c + 1),
(map) -> {
Vector.Builder b = Vec.inferringBuilder();
Index.Builder ib = new HashIndex.Builder();
for (Map.Entry<T, Integer> e : map.entrySet()) {
b.add(e.getValue());
ib.add(e.getKey());
}
Vector v = b.build();
v.setIndex(ib.build());
return v;
});
}
public static <T> Aggregator<T, Vector, ?> unique() {
return Aggregator.of(
HashSet::new, HashSet::add, (set) -> Vec.inferringBuilder().addAll(set).build());
}