Uses of Interface org.apache.hadoop.mapred.Reducer (Apache Hadoop Main 3.5.0 API)
Description: use: package: org.apache.hadoop.mapred, interface: Reducer

# Uses of Interface
org.apache.hadoop.mapred.Reducer

Packages that use Reducer
Package
Description
org.apache.hadoop.mapred
org.apache.hadoop.mapred.lib
org.apache.hadoop.mapred.lib.aggregate

- ## Uses of Reducer in org.apache.hadoop.mapred

  Methods in org.apache.hadoop.mapred that return types with arguments of type Reducer
  Modifier and Type
  Method
  Description
  `Class<? extends Reducer>`
  JobConf.`getCombinerClass()`
  Get the user-defined combiner class used to combine map-outputs before being sent to the reducers.
  `Class<? extends Reducer>`
  JobConf.`getReducerClass()`
  Get the `Reducer` class for the job.
  Method parameters in org.apache.hadoop.mapred with type arguments of type Reducer
  Modifier and Type
  Method
  Description
  `void`
  JobConf.`setCombinerClass(Class<? extends Reducer> theClass)`
  Set the user-defined combiner class used to combine map-outputs before being sent to the reducers.
  `void`
  JobConf.`setReducerClass(Class<? extends Reducer> theClass)`
  Set the `Reducer` class for the job.

- ## Uses of Reducer in org.apache.hadoop.mapred.lib

  Classes in org.apache.hadoop.mapred.lib that implement Reducer
  Modifier and Type
  Class
  Description
  `class`
  `ChainReducer`
  The ChainReducer class allows to chain multiple Mapper classes after a Reducer within the Reducer task.
  `class`
  `FieldSelectionMapReduce<K,V>`
  This class implements a mapper/reducer class that can be used to perform field selections in a manner similar to unix cut.
  `class`
  `IdentityReducer<K,V>`
  Performs no reduction, writing all input values directly to the output.
  `class`
  `LongSumReducer<K>`
  A `Reducer` that sums long values.
  Method parameters in org.apache.hadoop.mapred.lib with type arguments of type Reducer
  Modifier and Type
  Method
  Description
  `static <K1, V1, K2, V2>
  void`
  ChainReducer.`setReducer(JobConf job, Class<? extends Reducer<K1,V1,K2,V2>> klass, Class<? extends K1> inputKeyClass, Class<? extends V1> inputValueClass, Class<? extends K2> outputKeyClass, Class<? extends V2> outputValueClass, boolean byValue, JobConf reducerConf)`
  Sets the Reducer class to the chain job's JobConf.

- ## Uses of Reducer in org.apache.hadoop.mapred.lib.aggregate

  Classes in org.apache.hadoop.mapred.lib.aggregate that implement Reducer
  Modifier and Type
  Class
  Description
  `class`
  `ValueAggregatorCombiner<K1 extends WritableComparable,V1 extends Writable>`
  This class implements the generic combiner of Aggregate.
  `class`
  `ValueAggregatorJobBase<K1 extends WritableComparable,V1 extends Writable>`
  This abstract class implements some common functionalities of the the generic mapper, reducer and combiner classes of Aggregate.
  `class`
  `ValueAggregatorMapper<K1 extends WritableComparable,V1 extends Writable>`
  This class implements the generic mapper of Aggregate.
  `class`
  `ValueAggregatorReducer<K1 extends WritableComparable,V1 extends Writable>`
  This class implements the generic reducer of Aggregate.