org.apache.tinkerpop.gremlin.process.traversal.step.map

Class GroupCountStep.GroupCountMapReduce<E>

java.lang.Object

org.apache.tinkerpop.gremlin.process.computer.util.StaticMapReduce<E,Long,E,Long,Map<E,Long>>

org.apache.tinkerpop.gremlin.process.traversal.step.map.GroupCountStep.GroupCountMapReduce<E>

All Implemented Interfaces:

Cloneable, MapReduce<E,Long,E,Long,Map<E,Long>>

Enclosing class:

GroupCountStep<S,E>

public static final class GroupCountStep.GroupCountMapReduce<E>
extends StaticMapReduce<E,Long,E,Long,Map<E,Long>>

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.tinkerpop.gremlin.process.computer.MapReduce

MapReduce.MapEmitter<K,V>, MapReduce.NullObject, MapReduce.ReduceEmitter<OK,OV>, MapReduce.Stage

Field Summary

Fields inherited from interface org.apache.tinkerpop.gremlin.process.computer.MapReduce

MAP_REDUCE

Method Summary

Modifier and Type	Method and Description
void	combine(E key, Iterator<Long> values, MapReduce.ReduceEmitter<E,Long> emitter) The combine() method is logically executed at all "machines" in parallel.
boolean	doStage(MapReduce.Stage stage) A MapReduce job can be map-only, map-reduce-only, or map-combine-reduce.
Map<E,Long>	generateFinalResult(Iterator<KeyValue<E,Long>> keyValues) The key/value pairs emitted by reduce() (or map() in a map-only job) can be iterated to generate a local JVM Java object.
String	getMemoryKey() The results of the MapReduce job are associated with a memory-key to ultimately be stored in Memory.
static <E> GroupCountStep.GroupCountMapReduce<E>	instance()
void	map(Vertex vertex, MapReduce.MapEmitter<E,Long> emitter) The map() method is logically executed at all vertices in the graph in parallel.
void	reduce(E key, Iterator<Long> values, MapReduce.ReduceEmitter<E,Long> emitter) The reduce() method is logically on the "machine" the respective key hashes to.

Methods inherited from class org.apache.tinkerpop.gremlin.process.computer.util.StaticMapReduce

clone, equals, hashCode, storeState, toString

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface org.apache.tinkerpop.gremlin.process.computer.MapReduce

addResultToMemory, createMapReduce, getMapKeySort, getReduceKeySort, loadState, workerEnd, workerStart

Method Detail

doStage

public boolean doStage(MapReduce.Stage stage)

Description copied from interface: MapReduce

A MapReduce job can be map-only, map-reduce-only, or map-combine-reduce. Before executing the particular stage, this method is called to determine if the respective stage is defined. This method should return true if the respective stage as a non-default method implementation.

Parameters:

stage - the stage to check for definition.

Returns:

whether that stage should be executed.

map

public void map(Vertex vertex,
                MapReduce.MapEmitter<E,Long> emitter)

Description copied from interface: MapReduce

The map() method is logically executed at all vertices in the graph in parallel. The map() method emits key/value pairs given some analysis of the data in the vertices (and/or its incident edges).

Parameters:

vertex - the current vertex being map() processed.

emitter - the component that allows for key/value pairs to be emitted to the next stage.

reduce

public void reduce(E key,
                   Iterator<Long> values,
                   MapReduce.ReduceEmitter<E,Long> emitter)

Description copied from interface: MapReduce

The reduce() method is logically on the "machine" the respective key hashes to. The reduce() method combines all the values associated with the key and emits key/value pairs.

Parameters:

key - the key that has aggregated values

values - the aggregated values associated with the key

emitter - the component that allows for key/value pairs to be emitted as the final result.

combine

public void combine(E key,
                    Iterator<Long> values,
                    MapReduce.ReduceEmitter<E,Long> emitter)

Description copied from interface: MapReduce

The combine() method is logically executed at all "machines" in parallel. The combine() method pre-combines the values for a key prior to propagation over the wire. The combine() method must emit the same key/value pairs as the reduce() method. If there is a combine() implementation, there must be a reduce() implementation. If the MapReduce implementation is single machine, it can skip executing this method as reduce() is sufficient.

Parameters:

key - the key that has aggregated values

values - the aggregated values associated with the key

emitter - the component that allows for key/value pairs to be emitted to the reduce stage.

generateFinalResult

public Map<E,Long> generateFinalResult(Iterator<KeyValue<E,Long>> keyValues)

Description copied from interface: MapReduce

The key/value pairs emitted by reduce() (or map() in a map-only job) can be iterated to generate a local JVM Java object.

Parameters:

keyValues - the key/value pairs that were emitted from reduce() (or map() in a map-only job)

Returns:

the resultant object formed from the emitted key/values.

getMemoryKey

public String getMemoryKey()

Description copied from interface: MapReduce

The results of the MapReduce job are associated with a memory-key to ultimately be stored in Memory.

Returns:

the memory key of the generated result object.

instance

public static final <E> GroupCountStep.GroupCountMapReduce<E> instance()