| Package | Description | 
|---|---|
| org.apache.hadoop.mapred | |
| org.apache.hadoop.mapred.lib | |
| org.apache.hadoop.mapred.lib.aggregate | 
| Modifier and Type | Method and 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  Reducerclass for the job. | 
| Modifier and Type | Method and 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  Reducerclass for the job. | 
| Modifier and Type | Class and Description | 
|---|---|
| class  | ChainReducerThe 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  Reducerthat sums long values. | 
| Modifier and Type | Method and Description | 
|---|---|
| static <K1,V1,K2,V2> | 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. | 
| Modifier and Type | Class and 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. | 
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