private static <E> PCollection<E> partition(PCollection<E> collection, int numReducers) {
PType<E> type = collection.getPType();
PTableType<E, Void> tableType = Avros.tableOf(type, Avros.nulls());
PTable<E, Void> table = collection.parallelDo(new AsKeyTable<E>(), tableType);
PGroupedTable<E, Void> grouped =
numReducers > 0 ? table.groupByKey(numReducers) : table.groupByKey();
return grouped.ungroup().keys();
}
/** Returns the smallest numerical element from the input collection. */
public static <S> PObject<S> min(PCollection<S> collect) {
Class<S> clazz = collect.getPType().getTypeClass();
if (!clazz.isPrimitive() && !Comparable.class.isAssignableFrom(clazz)) {
throw new IllegalArgumentException(
"Can only get min for Comparable elements, not for: "
+ collect.getPType().getTypeClass());
}
PTypeFamily tf = collect.getTypeFamily();
PCollection<S> minCollect =
PTables.values(
collect
.parallelDo(
"min",
new DoFn<S, Pair<Boolean, S>>() {
private transient S min = null;
public void process(S input, Emitter<Pair<Boolean, S>> emitter) {
if (min == null || ((Comparable<S>) min).compareTo(input) > 0) {
min = input;
}
}
public void cleanup(Emitter<Pair<Boolean, S>> emitter) {
if (min != null) {
emitter.emit(Pair.of(false, min));
}
}
},
tf.tableOf(tf.booleans(), collect.getPType()))
.groupByKey()
.combineValues(
new CombineFn<Boolean, S>() {
public void process(
Pair<Boolean, Iterable<S>> input, Emitter<Pair<Boolean, S>> emitter) {
S min = null;
for (S v : input.second()) {
if (min == null || ((Comparable<S>) min).compareTo(v) > 0) {
min = v;
}
}
emitter.emit(Pair.of(input.first(), min));
}
}));
return new FirstElementPObject<S>(minCollect);
}
/**
* Returns a {@code PTable} that contains the unique elements of this collection mapped to a count
* of their occurrences.
*/
public static <S> PTable<S, Long> count(PCollection<S> collect) {
PTypeFamily tf = collect.getTypeFamily();
return collect
.parallelDo(
"Aggregate.count",
new MapFn<S, Pair<S, Long>>() {
public Pair<S, Long> map(S input) {
return Pair.of(input, 1L);
}
},
tf.tableOf(collect.getPType(), tf.longs()))
.groupByKey()
.combineValues(Aggregators.SUM_LONGS());
}