/**
* 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());
}
/**
* Returns the number of elements in the provided PCollection.
*
* @param collect The PCollection whose elements should be counted.
* @param <S> The type of the PCollection.
* @return A {@code PObject} containing the number of elements in the {@code PCollection}.
*/
public static <S> PObject<Long> length(PCollection<S> collect) {
PTypeFamily tf = collect.getTypeFamily();
PTable<Integer, Long> countTable =
collect
.parallelDo(
"Aggregate.count",
new MapFn<S, Pair<Integer, Long>>() {
public Pair<Integer, Long> map(S input) {
return Pair.of(1, 1L);
}
},
tf.tableOf(tf.ints(), tf.longs()))
.groupByKey()
.combineValues(Aggregators.SUM_LONGS());
PCollection<Long> count = countTable.values();
return new FirstElementPObject<Long>(count);
}
@Override
public PTable<K, V> combineValues(Aggregator<V> combineAgg, Aggregator<V> reduceAgg) {
return combineValues(
Aggregators.<K, V>toCombineFn(combineAgg, parent.getValueType()),
Aggregators.<K, V>toCombineFn(reduceAgg, parent.getValueType()));
}