com.google.cloud.dataflow.sdk.transforms

Class Combine.PerKey<K,InputT,OutputT>

java.lang.Object

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

com.google.cloud.dataflow.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

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>perKey(
         new Sum.SumDoubleFn()));
  

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 com.google.cloud.dataflow.sdk.transforms.PTransform

name

Method Summary

Modifier and Type	Method and Description
PCollection<KV<K,OutputT>>	apply(PCollection<KV<K,InputT>> input) Applies this PTransform on the given InputT, and returns its Output.
CombineFnBase.PerKeyCombineFn<? super K,? super InputT,?,OutputT>	getFn() Returns the CombineFnBase.PerKeyCombineFn used by this Combine operation.
List<PCollectionView<?>>	getSideInputs() Returns the side inputs used by this Combine operation.
Combine.PerKey<K,InputT,OutputT>	named(String name) Return a new Globally transform that's like this transform but with the specified name.
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.KeyedCombineFnWithContext.

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.PerKey<K,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.

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.KeyedCombineFnWithContext.

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.PerKeyCombineFn<? super K,? super InputT,?,OutputT> getFn()

Returns the CombineFnBase.PerKeyCombineFn used by this Combine operation.

getSideInputs

public List<PCollectionView<?>> getSideInputs()

Returns the side inputs used by this Combine operation.

apply

public PCollection<KV<K,OutputT>> apply(PCollection<KV<K,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<KV<K,InputT>>,PCollection<KV<K,OutputT>>>