Package org.apache.beam.sdk.extensions.zetasketch

Class HllCount.Extract

java.lang.Object

org.apache.beam.sdk.extensions.zetasketch.HllCount.Extract

Enclosing class:

HllCount

public static final class HllCount.Extract
extends Object

Provides PTransforms to extract the estimated count of distinct elements (as Longs) from each HLL++ sketch.

When extracting from an "empty sketch" represented by an byte array of length 0, the result returned is 0.

Corresponds to the HLL_COUNT.EXTRACT(sketch) function in BigQuery.

Method Summary

Modifier and Type	Method	Description
static PTransform<PCollection<byte[]>,PCollection<Long>>	globally()	Returns a PTransform that takes an input PCollection<byte[]> of HLL++ sketches and returns a PCollection<Long> of the estimated count of distinct elements extracted from each sketch.
static <K> PTransform<PCollection<KV<K,byte[]>>,PCollection<KV<K,Long>>>	perKey()	Returns a PTransform that takes an input PCollection<KV<K, byte[]>> of (key, HLL++ sketch) pairs and returns a PCollection<KV<K, Long>> of (key, estimated count of distinct elements extracted from each sketch).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

globally

public static PTransform<PCollection<byte[]>,PCollection<Long>> globally()

Returns a PTransform that takes an input PCollection<byte[]> of HLL++ sketches and returns a PCollection<Long> of the estimated count of distinct elements extracted from each sketch.

Returns 0 if the input element is an "empty sketch" (byte array of length 0).

perKey

public static <K>
PTransform<PCollection<KV<K,byte[]>>,PCollection<KV<K,Long>>> perKey()

Returns a PTransform that takes an input PCollection<KV<K, byte[]>> of (key, HLL++ sketch) pairs and returns a PCollection<KV<K, Long>> of (key, estimated count of distinct elements extracted from each sketch).