com.google.cloud.dataflow.sdk.transforms

Class Count

java.lang.Object

com.google.cloud.dataflow.sdk.transforms.Count

public class Count
extends java.lang.Object

Count<T> takes a PCollection<T> and returns a PCollection<KV<T, Long>> representing a map from each distinct element of the input PCollection to the number of times that element occurs in the input. Each of the keys in the output PCollection is unique.

Two values of type T are compared for equality not by regular Java Object.equals(java.lang.Object), but instead by first encoding each of the elements using the PCollection's Coder, and then comparing the encoded bytes. This admits efficient parallel evaluation.

By default, the Coder of the keys of the output PCollection is the same as the Coder of the elements of the input PCollection.

Each output element is in the window by which its corresponding input was grouped, and has the timestamp of the end of that window. The output PCollection has the same WindowFn as the input.

Example of use:

 PCollection<String> words = ...;
 PCollection<KV<String, Long>> wordCounts =
     words.apply(Count.<String>perElement());
  

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Count.Globally<T> Count.Globally<T> takes a PCollection<T> and returns a PCollection<Long> containing a single element which is the total number of elements in the PCollection.
static class	Count.PerElement<T> Count.PerElement<T> takes a PCollection<T> and returns a PCollection<KV<T, Long>> representing a map from each distinct element of the input PCollection to the number of times that element occurs in the input.

Constructor Summary

Constructors

Constructor and Description
Count()

Method Summary

Methods

Modifier and Type	Method and Description
static <T> Count.Globally<T>	globally() Returns a Count.Globally PTransform that counts the number of elements in its input PCollection.
static <T> Count.PerElement<T>	perElement() Returns a Count.PerElement PTransform that counts the number of occurrences of each element in its input PCollection.

Methods inherited from class java.lang.Object

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

Constructor Detail

Count

public Count()

Method Detail

globally

public static <T> Count.Globally<T> globally()

Returns a Count.Globally PTransform that counts the number of elements in its input PCollection.

See Count.Globally for more details.

perElement

public static <T> Count.PerElement<T> perElement()

Returns a Count.PerElement PTransform that counts the number of occurrences of each element in its input PCollection.

See Count.PerElement for more details.