com.google.cloud.dataflow.sdk.transforms

Class Combine.PerKey<K,VI,VO>

java.lang.Object

com.google.cloud.dataflow.sdk.transforms.PTransform<PCollection<KV<K,VI>>,PCollection<KV<K,VO>>>

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

Type Parameters:

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

VI - the type of the values of the input PCollection

VO - the type of the values of the output PCollection

All Implemented Interfaces:

java.io.Serializable

Enclosing class:

Combine

public static class Combine.PerKey<K,VI,VO>
extends PTransform<PCollection<KV<K,VI>>,PCollection<KV<K,VO>>>

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

Methods

Modifier and Type	Method and Description
PCollection<KV<K,VO>>	apply(PCollection<KV<K,VI>> input) Applies this PTransform on the given Input, and returns its Output.
Combine.KeyedCombineFn<? super K,? super VI,?,VO>	getFn() Returns the KeyedCombineFn used by this Combine operation.
protected java.lang.String	getKindString() Returns a string describing what kind of PTransform this is.
Combine.PerKeyWithHotKeys<K,VI,VO>	withHotKeys(int hotKeySpread) Like withHotKeys(SerializableFunction), but returning the given constant value for every key.
Combine.PerKeyWithHotKeys<K,VI,VO>	withHotKeys(SerializableFunction<? super K,java.lang.Integer> hotKeySpread) If a single key has disproportionately many values, it may become a bottleneck, especially in streaming mode.
Combine.PerKey<K,VI,VO>	withName(java.lang.String name) Sets the base name of this PTransform and returns itself.

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

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

Methods inherited from class java.lang.Object

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

Method Detail

withHotKeys

public Combine.PerKeyWithHotKeys<K,VI,VO> withHotKeys(SerializableFunction<? super K,java.lang.Integer> hotKeySpread)

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:

hotKeySpread - 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.

withHotKeys

public Combine.PerKeyWithHotKeys<K,VI,VO> withHotKeys(int hotKeySpread)

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

withName

public Combine.PerKey<K,VI,VO> withName(java.lang.String name)

Description copied from class: PTransform

Sets the base name of this PTransform and returns itself.

This is a shortcut for calling PTransform.setName(java.lang.String), which allows method chaining.

Overrides:

withName in class PTransform<PCollection<KV<K,VI>>,PCollection<KV<K,VO>>>

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<KV<K,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<KV<K,VI>>,PCollection<KV<K,VO>>>

getKindString

protected java.lang.String getKindString()

Description copied from class: PTransform

Returns a string describing what kind of PTransform this is.

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

Overrides:

getKindString in class PTransform<PCollection<KV<K,VI>>,PCollection<KV<K,VO>>>