com.google.cloud.dataflow.sdk.transforms

Class Combine.Globally<InputT,OutputT>

java.lang.Object

com.google.cloud.dataflow.sdk.transforms.PTransform<PCollection<InputT>,PCollection<OutputT>>

com.google.cloud.dataflow.sdk.transforms.Combine.Globally<InputT,OutputT>

Type Parameters:

InputT - type of input values

OutputT - type of output values

All Implemented Interfaces:

Serializable

Enclosing class:

Combine

public static class Combine.Globally<InputT,OutputT>
extends PTransform<PCollection<InputT>,PCollection<OutputT>>

Combine.Globally<InputT, OutputT> takes a PCollection<InputT> and returns a PCollection<OutputT> whose elements are the result of combining all the elements in each window of the input PCollection, using a specified CombineFn<InputT, AccumT, OutputT>. It is common for InputT == OutputT, 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<Integer> pc = ...;
 PCollection<Integer> sum = pc.apply(
     Combine.globally(new Sum.SumIntegerFn()));
  

Combining can happen in parallel, with different subsets of the input PCollection being combined separately, and their intermediate results combined further, in an arbitrary tree reduction pattern, until a single result value is produced.

If the input PCollection is windowed into GlobalWindows, a default value in the GlobalWindow will be output if the input PCollection is empty. To use this with inputs with other windowing, either withoutDefaults() or asSingletonView() must be called.

By default, the Coder of the output PValue<OutputT> is inferred from the concrete type of the CombineFn<InputT, AccumT, OutputT>'s output type OutputT.

See also Combine.perKey(com.google.cloud.dataflow.sdk.transforms.SerializableFunction<java.lang.Iterable<V>, V>)/Combine.PerKey and Combine.groupedValues(com.google.cloud.dataflow.sdk.transforms.SerializableFunction<java.lang.Iterable<V>, V>)/Combine.GroupedValues, which are useful for combining values associated with each key in a PCollection of KVs.

See Also:

Serialized Form

Field Summary

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

name

Method Summary

Modifier and Type	Method and Description
PCollection<OutputT>	apply(PCollection<InputT> input) Applies this PTransform on the given InputT, and returns its Output.
Combine.GloballyAsSingletonView<InputT,OutputT>	asSingletonView() Returns a PTransform that produces a PCollectionView whose elements are the result of combining elements per-window in the input PCollection.
Combine.Globally<InputT,OutputT>	named(String name) Return a new Globally transform that's like this transform but with the specified name.
Combine.Globally<InputT,OutputT>	withFanout(int fanout) Returns a PTransform identical to this, but that uses an intermediate node to combine parts of the data to reduce load on the final global combine step.
Combine.Globally<InputT,OutputT>	withoutDefaults() Returns a PTransform identical to this, but that does not attempt to provide a default value in the case of empty input.

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

getDefaultOutputCoder, getDefaultOutputCoder, getDefaultOutputCoder, getKindString, getName, toString, validate

Methods inherited from class java.lang.Object

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

Method Detail

named

public Combine.Globally<InputT,OutputT> named(String name)

Return a new Globally transform that's like this transform but with the specified name. Does not modify this transform.

asSingletonView

public Combine.GloballyAsSingletonView<InputT,OutputT> asSingletonView()

Returns a PTransform that produces a PCollectionView whose elements are the result of combining elements per-window in the input PCollection. If a value is requested from the view for a window that is not present, the result of calling the CombineFn on empty input will returned.

withoutDefaults

public Combine.Globally<InputT,OutputT> withoutDefaults()

Returns a PTransform identical to this, but that does not attempt to provide a default value in the case of empty input.

withFanout

public Combine.Globally<InputT,OutputT> withFanout(int fanout)

Returns a PTransform identical to this, but that uses an intermediate node to combine parts of the data to reduce load on the final global combine step.

The fanout parameter determines the number of intermediate keys that will be used.

apply

public PCollection<OutputT> apply(PCollection<InputT> input)

Description copied from class: PTransform

Applies this PTransform on the given InputT, 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<InputT, OutputT>, InputT).

Overrides:

apply in class PTransform<PCollection<InputT>,PCollection<OutputT>>