public static Aggregator<Object, String, ?> join(
CharSequence delimit, CharSequence prefix, CharSequence suffix) {
return Aggregator.of(
() -> new StringJoiner(delimit, prefix, suffix),
(j, s) -> j.add(!Is.NA(s) ? s.toString() : "NA"),
StringJoiner::toString);
}
/** @return an aggregator that computes the median. */
public static Aggregator<Number, Double, ?> median() {
Aggregator<Number, Double, ? extends List<Number>> of =
Aggregator.of(
ArrayList::new,
ArrayList::add,
(list) -> {
int size = list.size();
if (size == 0) {
return Na.from(Double.class);
} else if (size == 1) {
return list.get(0).doubleValue();
} else if (size == 2) {
return (list.get(0).doubleValue() + list.get(1).doubleValue()) / 2;
} else {
Collections.sort(list, (a, b) -> Double.compare(a.doubleValue(), b.doubleValue()));
int index = (size - 1) / 2;
if (size % 2 == 0) {
return (list.get(index).doubleValue() + list.get(index + 1).doubleValue()) / 2;
} else {
return list.get(index).doubleValue();
}
}
});
return of;
}
public static <T> Aggregator<T, Integer, ?> count() {
return Aggregator.of(
() -> new int[1],
(int[] a, T b) -> {
if (!Is.NA(b)) {
a[0] += 1;
}
},
(int[] a) -> a[0]);
}
public static Aggregator<Number, Double, ?> sum() {
return Aggregator.of(
() -> new double[0],
(s, v) -> {
if (!Is.NA(v)) {
s[0] += v.doubleValue();
}
},
s -> s[0]);
}
/**
* @param copies the number of copies of each element
* @return an aggregator that repeats each value {@code copies} times.
*/
public static <T> Aggregator<T, Vector, ?> each(Supplier<Vector.Builder> vb, int copies) {
return Aggregator.of(
vb,
(acc, v) -> {
for (int i = 0; i < copies; i++) {
acc.add(v);
}
},
Vector.Builder::build);
}
/**
* Returns an aggregator that is able to filter values.
*
* @param supplier the vector builder
* @param predicate the predicate. If {@code true} include value.
* @param <T> the input type
* @return a filtering aggregator
*/
public static <T> Aggregator<T, Vector, ?> filter(
Supplier<Vector.Builder> supplier, Predicate<T> predicate) {
return Aggregator.of(
supplier,
(acc, v) -> {
if (predicate.test(v)) {
acc.add(v);
}
},
Vector.Builder::build);
}
public static Aggregator<Number, Double, ?> var() {
return Aggregator.of(
FastStatistics::new,
(a, v) -> {
if (!Is.NA(v)) {
a.addValue(v.doubleValue());
}
},
(stat) -> {
if (stat.getN() == 0) {
return Na.from(Double.class);
}
return stat.getVariance();
});
}
public static <T> Aggregator<T, Vector, ?> repeat(Supplier<Vector.Builder> vb, int copies) {
return Aggregator.of(
vb,
Vector.Builder::add,
(v) -> {
Vector temp = v.getTemporaryVector();
int size = temp.size();
for (int i = 1; i < copies; i++) {
for (int j = 0; j < size; j++) {
v.add(temp, j);
}
}
return v.build();
});
}
public static Aggregator<Number, Number, ?> min() {
return Aggregator.of(
FastStatistics::new,
(a, v) -> {
if (!Is.NA(v)) {
a.addValue(v.doubleValue());
}
},
(r) -> {
if (r.getN() == 0) {
return Na.from(Double.class);
} else {
return r.getMin();
}
});
}
public static Aggregator<Double, Double, ?> max() {
return Aggregator.of(
FastStatistics::new,
(a, v) -> {
if (!Is.NA(v)) {
a.addValue(v);
}
},
(r) -> {
if (r.getN() == 0) {
return Na.from(Double.class);
} else {
return r.getMax();
}
});
}
public static <T> Aggregator<T, T, ?> reducing(BinaryOperator<T> operator) {
class Value implements Consumer<T> {
private T value;
@Override
public void accept(T t) {
if (value == null) {
value = t;
} else {
operator.apply(value, t);
}
}
}
return Aggregator.of(Value::new, Value::accept, (acc) -> acc.value);
}
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, Map<T, Double>, ?> normalizedValueCounts() {
class MapCounter {
private HashMap<T, Integer> map = new HashMap<>();
private int count = 0;
}
return Aggregator.of(
MapCounter::new,
new BiConsumer<MapCounter, T>() {
@Override
public void accept(MapCounter mapCounter, T t) {
mapCounter.count++;
mapCounter.map.compute(t, (v, c) -> c == null ? 1 : c + 1);
}
},
mapCounter -> {
Map<T, Double> map = new HashMap<>();
mapCounter
.map
.entrySet()
.forEach(e -> map.put(e.getKey(), e.getValue() / (double) mapCounter.count));
return map;
});
}
/**
* Performs a transformation operation, mapping each element to a new value, adding it to the
* {@code Vector.Builder} finishing it constructing a new {@code Vector}.
*
* @param supplier supply the vector builder
* @param function the mapper
* @param <T> the input type
* @param <O> the output type
* @return a transformation aggregator
*/
public static <T, O> Aggregator<T, Vector, ?> transform(
Supplier<Vector.Builder> supplier, Function<? super T, ? extends O> function) {
return Aggregator.of(supplier, (acc, v) -> acc.add(function.apply(v)), Vector.Builder::build);
}
public static <T> Aggregator<T, Integer, ?> nunique() {
return Aggregator.of(HashSet::new, HashSet::add, HashSet::size);
}
public static <T> Aggregator<T, Vector, ?> unique() {
return Aggregator.of(
HashSet::new, HashSet::add, (set) -> Vec.inferringBuilder().addAll(set).build());
}
