com.google.cloud.dataflow.sdk.transforms

Class Combine.GroupedValues<K,VI,VO>

java.lang.Object

com.google.cloud.dataflow.sdk.transforms.PTransform<PCollection<? extends KV<K,? extends java.lang.Iterable<VI>>>,PCollection<KV<K,VO>>>

com.google.cloud.dataflow.sdk.transforms.Combine.GroupedValues<K,VI,VO>

Type Parameters:

K - type of input and output keys

VI - type of input values

VO - type of output values

All Implemented Interfaces:

java.io.Serializable

Enclosing class:

Combine

public static class Combine.GroupedValues<K,VI,VO>
extends PTransform<PCollection<? extends KV<K,? extends java.lang.Iterable<VI>>>,PCollection<KV<K,VO>>>

GroupedValues<K, VI, VO> takes a PCollection<KV<K, Iterable<VI>>>, such as the result of GroupByKey, applies a specified KeyedCombineFn<K, VI, VA, VO> to each of the input KV<K, Iterable<VI>> elements to produce a combined output KV<K, VO> element, and returns a PCollection<KV<K, VO>> containing all the combined output elements. It is common for VI == VO, but not required. Common combining functions include sums, mins, maxes, and averages of numbers, conjunctions and disjunctions of booleans, statistical aggregations, etc.

Example of use:

 PCollection<KV<String, Integer>> pc = ...;
 PCollection<KV<String, Iterable<Integer>>> groupedByKey = pc.apply(
     new GroupByKey<String, Integer>());
 PCollection<KV<String, Integer>> sumByKey = groupedByKey.apply(
     Combine.<String, Integer>groupedValues(
         new Sum.SumIntegerFn()));
  

See also Combine.perKey(com.google.cloud.dataflow.sdk.transforms.SerializableFunction<java.lang.Iterable<V>, V>)/Combine.PerKey which captures the common pattern of "combining by key" in a single easy-to-use PTransform.

Combining for different keys can happen in parallel. Moreover, combining of the Iterable<VI> values associated a single key can happen in parallel, with different subsets of the values being combined separately, and their intermediate results combined further, in an arbitrary tree reduction pattern, until a single result value is produced for each key.

By default, the Coder of the keys of the output PCollection<KV<K, VO>> is that of the keys of the input PCollection<KV<K, VI>>, and the Coder of the values of the output PCollection<KV<K, VO>> is inferred from the concrete type of the KeyedCombineFn<K, VI, VA, VO>'s output type VO.

Each output element has the same timestamp and is in the same window as its corresponding input element, and the output PCollection has the same WindowFn associated with it as the input.

See also Combine.globally(com.google.cloud.dataflow.sdk.transforms.SerializableFunction<java.lang.Iterable<V>, V>)/Combine.Globally, which combines all the values in a PCollection into a single value in a PCollection.

See Also:

Serialized Form

Field Summary

Fields inherited from class com.google.cloud.dataflow.sdk.transforms.PTransform

name

Method Summary

Methods

Modifier and Type	Method and Description
PCollection<KV<K,VO>>	apply(PCollection<? extends KV<K,? extends java.lang.Iterable<VI>>> input) Applies this PTransform on the given Input, and returns its Output.
Coder<?>	getAccumulatorCoder()
Coder<KV<K,VO>>	getDefaultOutputCoder() Returns the default Coder to use for the output of this single-output PTransform, or null if none can be inferred.
Combine.KeyedCombineFn<? super K,? super VI,?,VO>	getFn() Returns the KeyedCombineFn used by this Combine operation.

Methods inherited from class com.google.cloud.dataflow.sdk.transforms.PTransform

finishSpecifying, getCoderRegistry, getDefaultName, getDefaultOutputCoder, getInput, getKindString, getName, getOutput, getPipeline, setName, setPipeline, toString, withName

Methods inherited from class java.lang.Object

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

Method Detail

getFn

public Combine.KeyedCombineFn<? super K,? super VI,?,VO> getFn()

Returns the KeyedCombineFn used by this Combine operation.

apply

public PCollection<KV<K,VO>> apply(PCollection<? extends KV<K,? extends java.lang.Iterable<VI>>> input)

Description copied from class: PTransform

Applies this PTransform on the given Input, and returns its Output.

Composite transforms, which are defined in terms of other transforms, should return the output of one of the composed transforms. Non-composite transforms, which do not apply any transforms internally, should return a new unbound output and register evaluators (via backend-specific registration methods).

The default implementation throws an exception. A derived class must either implement apply, or else each runner must supply a custom implementation via PipelineRunner.apply(com.google.cloud.dataflow.sdk.transforms.PTransform<Input, Output>, Input).

Overrides:

apply in class PTransform<PCollection<? extends KV<K,? extends java.lang.Iterable<VI>>>,PCollection<KV<K,VO>>>

getAccumulatorCoder

public Coder<?> getAccumulatorCoder()

getDefaultOutputCoder

public Coder<KV<K,VO>> getDefaultOutputCoder()

Description copied from class: PTransform

Returns the default Coder to use for the output of this single-output PTransform, or null if none can be inferred.

By default, returns null.

Overrides:

getDefaultOutputCoder in class PTransform<PCollection<? extends KV<K,? extends java.lang.Iterable<VI>>>,PCollection<KV<K,VO>>>