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

Packages that use Reducer
org.apache.hadoop.contrib.index.mapred
org.apache.hadoop.contrib.utils.join
org.apache.hadoop.examples: Hadoop example code.
org.apache.hadoop.mapred: A software framework for easily writing applications which process vast amounts of data (multi-terabyte data-sets) parallelly on large clusters (thousands of nodes) built of commodity hardware in a reliable, fault-tolerant manner.
org.apache.hadoop.mapred.lib: Library of generally useful mappers, reducers, and partitioners.
org.apache.hadoop.mapred.lib.aggregate: Classes for performing various counting and aggregations.
org.apache.hadoop.streaming: `Hadoop Streaming` is a utility which allows users to create and run Map-Reduce jobs with any executables (e.g.

Uses of Reducer in org.apache.hadoop.contrib.index.mapred

Classes in org.apache.hadoop.contrib.index.mapred that implement Reducer
`class` `IndexUpdateCombiner` This combiner combines multiple intermediate forms into one intermediate form.
`class` `IndexUpdateReducer` This reducer applies to a shard the changes for it.

Uses of Reducer in org.apache.hadoop.contrib.utils.join

Classes in org.apache.hadoop.contrib.utils.join that implement Reducer
`class` `DataJoinMapperBase` This abstract class serves as the base class for the mapper class of a data join job.
`class` `DataJoinReducerBase` This abstract class serves as the base class for the reducer class of a data join job.
`class` `JobBase` A common base implementing some statics collecting mechanisms that are commonly used in a typical map/reduce job.

Uses of Reducer in org.apache.hadoop.examples

Classes in org.apache.hadoop.examples that implement Reducer
`static class` `PiEstimator.PiReducer` Reducer class for Pi estimation.
`class` `SleepJob` Dummy class for testing MR framefork.

Uses of Reducer in org.apache.hadoop.mapred

Methods in org.apache.hadoop.mapred that return types with arguments of type Reducer
`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
`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.

Constructor parameters in org.apache.hadoop.mapred with type arguments of type Reducer
`Task.OldCombinerRunner(Class<? extends Reducer<K,V,K,V>> cls, JobConf conf, Counters.Counter inputCounter, Task.TaskReporter reporter)`

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

Classes in org.apache.hadoop.mapred.lib that implement Reducer
`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

`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
`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.

Uses of Reducer in org.apache.hadoop.streaming

Classes in org.apache.hadoop.streaming that implement Reducer
`class` `PipeCombiner`
`class` `PipeReducer` A generic Reducer bridge.

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