Package org.apache.beam.sdk.transforms

Class Combine.PerKey<K,InputT,OutputT>

java.lang.Object

org.apache.beam.sdk.transforms.PTransform<PCollection<KV<K,InputT>>,PCollection<KV<K,OutputT>>>

org.apache.beam.sdk.transforms.Combine.PerKey<K,InputT,OutputT>

Type Parameters:

K - the type of the keys of the input and output PCollections

InputT - the type of the values of the input PCollection

OutputT - the type of the values of the output PCollection

All Implemented Interfaces:

Serializable, HasDisplayData

Enclosing class:

Combine

public static class Combine.PerKey<K,InputT,OutputT>
extends PTransform<PCollection<KV<K,InputT>>,PCollection<KV<K,OutputT>>>

PerKey<K, InputT, OutputT> takes a PCollection<KV<K, InputT>>, groups it by key, applies a combining function to the InputT values associated with each key to produce a combined OutputT value, and returns a PCollection<KV<K, OutputT>> representing a map from each distinct key of the input PCollection to the corresponding combined value. InputT and OutputT are often the same.

This is a concise shorthand for an application of GroupByKey followed by an application of Combine.GroupedValues. See those operations for more details on how keys are compared for equality and on the default Coder for the output.

Example of use:

 PCollection<KV<String, Double>> salesRecords = ...;
 PCollection<KV<String, Double>> totalSalesPerPerson =
     salesRecords.apply(Combine.<String, Double, Double>perKey(
         Sum.ofDoubles()));
 

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.

See Also:

• Serialized Form

Field Summary

Fields inherited from class org.apache.beam.sdk.transforms.PTransform

annotations, displayData, name, resourceHints

Method Summary

Modifier and Type	Method	Description
PCollection<KV<K,OutputT>>	expand(PCollection<KV<K,InputT>> input)	Override this method to specify how this PTransform should be expanded on the given InputT.
Map<TupleTag<?>,PValue>	getAdditionalInputs()	Returns the side inputs of this Combine, tagged with the tag of the PCollectionView.
CombineFnBase.GlobalCombineFn<? super InputT,?,OutputT>	getFn()	Returns the CombineFnBase.GlobalCombineFn used by this Combine operation.
protected String	getKindString()	Returns the name to use by default for this PTransform (not including the names of any enclosing PTransforms).
List<PCollectionView<?>>	getSideInputs()	Returns the side inputs used by this Combine operation.
void	populateDisplayData(DisplayData.Builder builder)	Register display data for the given transform or component.
Combine.PerKeyWithHotKeyFanout<K,InputT,OutputT>	withHotKeyFanout(int hotKeyFanout)	Like withHotKeyFanout(SerializableFunction), but returning the given constant value for every key.
Combine.PerKeyWithHotKeyFanout<K,InputT,OutputT>	withHotKeyFanout(SerializableFunction<? super K,Integer> hotKeyFanout)	If a single key has disproportionately many values, it may become a bottleneck, especially in streaming mode.
Combine.PerKey<K,InputT,OutputT>	withSideInputs(Iterable<? extends PCollectionView<?>> sideInputs)	Returns a PTransform identical to this, but with the specified side inputs to use in CombineWithContext.CombineFnWithContext.
Combine.PerKey<K,InputT,OutputT>	withSideInputs(PCollectionView<?>... sideInputs)	Returns a PTransform identical to this, but with the specified side inputs to use in CombineWithContext.CombineFnWithContext.

Methods inherited from class org.apache.beam.sdk.transforms.PTransform

addAnnotation, compose, compose, getAnnotations, getDefaultOutputCoder, getDefaultOutputCoder, getDefaultOutputCoder, getName, getResourceHints, setDisplayData, setResourceHints, toString, validate, validate

Methods inherited from class java.lang.Object

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

Method Details

getKindString

protected String getKindString()

Description copied from class: PTransform

Returns the name to use by default for this PTransform (not including the names of any enclosing PTransforms).

By default, returns the base name of this PTransform's class.

The caller is responsible for ensuring that names of applied PTransforms are unique, e.g., by adding a uniquifying suffix when needed.

Overrides:

getKindString in class PTransform<PCollection<KV<K,InputT>>,PCollection<KV<K,OutputT>>>

withSideInputs

public Combine.PerKey<K,InputT,OutputT> withSideInputs(PCollectionView<?>... sideInputs)

Returns a PTransform identical to this, but with the specified side inputs to use in CombineWithContext.CombineFnWithContext.

withSideInputs

public Combine.PerKey<K,InputT,OutputT> withSideInputs(Iterable<? extends PCollectionView<?>> sideInputs)

Returns a PTransform identical to this, but with the specified side inputs to use in CombineWithContext.CombineFnWithContext.

withHotKeyFanout

public Combine.PerKeyWithHotKeyFanout<K,InputT,OutputT> withHotKeyFanout(SerializableFunction<? super K,Integer> hotKeyFanout)

If a single key has disproportionately many values, it may become a bottleneck, especially in streaming mode. This returns a new per-key combining transform that inserts an intermediate node to combine "hot" keys partially before performing the full combine.

Parameters:

hotKeyFanout - a function from keys to an integer N, where the key will be spread among N intermediate nodes for partial combining. If N is less than or equal to 1, this key will not be sent through an intermediate node.

withHotKeyFanout

public Combine.PerKeyWithHotKeyFanout<K,InputT,OutputT> withHotKeyFanout(int hotKeyFanout)

Like withHotKeyFanout(SerializableFunction), but returning the given constant value for every key.

getFn

public CombineFnBase.GlobalCombineFn<? super InputT,?,OutputT> getFn()

Returns the CombineFnBase.GlobalCombineFn used by this Combine operation.

getSideInputs

public List<PCollectionView<?>> getSideInputs()

Returns the side inputs used by this Combine operation.

getAdditionalInputs

public Map<TupleTag<?>,PValue> getAdditionalInputs()

Returns the side inputs of this Combine, tagged with the tag of the PCollectionView. The values of the returned map will be equal to the result of getSideInputs().

Overrides:

getAdditionalInputs in class PTransform<PCollection<KV<K,InputT>>,PCollection<KV<K,OutputT>>>

expand

public PCollection<KV<K,OutputT>> expand(PCollection<KV<K,InputT>> input)

Description copied from class: PTransform

Override this method to specify how this PTransform should be expanded on the given InputT.

NOTE: This method should not be called directly. Instead apply the PTransform should be applied to the InputT using the apply method.

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).

Specified by:

expand in class PTransform<PCollection<KV<K,InputT>>,PCollection<KV<K,OutputT>>>

populateDisplayData

public void populateDisplayData(DisplayData.Builder builder)

Description copied from class: PTransform

Register display data for the given transform or component.

populateDisplayData(DisplayData.Builder) is invoked by Pipeline runners to collect display data via DisplayData.from(HasDisplayData). Implementations may call super.populateDisplayData(builder) in order to register display data in the current namespace, but should otherwise use subcomponent.populateDisplayData(builder) to use the namespace of the subcomponent.

By default, does not register any display data. Implementors may override this method to provide their own display data.

Specified by:

populateDisplayData in interface HasDisplayData

Overrides:

populateDisplayData in class PTransform<PCollection<KV<K,InputT>>,PCollection<KV<K,OutputT>>>

Parameters:

builder - The builder to populate with display data.

See Also:

• HasDisplayData