| Package | Description | 
|---|---|
| org.apache.hadoop.mapred | |
| org.apache.hadoop.mapred.lib | |
| org.apache.hadoop.mapred.lib.aggregate | 
| Modifier and Type | Interface and Description | 
|---|---|
| interface  | Mapper<K1,V1,K2,V2>Maps input key/value pairs to a set of intermediate key/value pairs. | 
| interface  | Reducer<K2,V2,K3,V3>Reduces a set of intermediate values which share a key to a smaller set of
 values. | 
| Modifier and Type | Class and Description | 
|---|---|
| class  | ChainMapperThe ChainMapper class allows to use multiple Mapper classes within a single
 Map task. | 
| 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  | IdentityMapper<K,V>Implements the identity function, mapping inputs directly to outputs. | 
| class  | IdentityReducer<K,V>Performs no reduction, writing all input values directly to the output. | 
| class  | InverseMapper<K,V>A  Mapperthat swaps keys and values. | 
| class  | LongSumReducer<K>A  Reducerthat sums long values. | 
| class  | RegexMapper<K>A  Mapperthat extracts text matching a regular expression. | 
| class  | TokenCountMapper<K>A  Mapperthat maps text values into <token,freq> pairs. | 
| 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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