org.apache.hadoop.mapred.lib.aggregate
Class ValueAggregatorReducer

java.lang.Object
  org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorJobBase
      org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorReducer

All Implemented Interfaces:

Closeable, JobConfigurable, Mapper, Reducer

public class ValueAggregatorReducer
extends ValueAggregatorJobBase

This class implements the generic reducer of Abacus.

Field Summary

Fields inherited from class org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorJobBase

aggregatorDescriptorList

Constructor Summary

ValueAggregatorReducer()

Method Summary

void	map(WritableComparable arg0, Writable arg1, OutputCollector arg2, Reporter arg3) Do nothing.
void	reduce(WritableComparable key, Iterator values, OutputCollector output, Reporter reporter) Combines values for a given key.

Methods inherited from class org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorJobBase

close, configure, logSpec

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ValueAggregatorReducer

public ValueAggregatorReducer()

Method Detail

reduce

public void reduce(WritableComparable key,
                   Iterator values,
                   OutputCollector output,
                   Reporter reporter)
            throws IOException

Description copied from interface: Reducer

Combines values for a given key. Output values must be of the same type as input values. Input keys must not be altered. Typically all values are combined into zero or one value. Output pairs are collected with calls to OutputCollector.collect(WritableComparable,Writable).

Parameters:

key - the key is expected to be a Text object, whose prefix indicates the type of aggregation to aggregate the values. In effect, data driven computing is achieved. It is assumed that each aggregator's getReport method emits appropriate output for the aggregator. This may be further customiized.

values - the values to combine

output - to collect combined values

Throws:

IOException

map

public void map(WritableComparable arg0,
                Writable arg1,
                OutputCollector arg2,
                Reporter arg3)
         throws IOException

Do nothing. Should not be called

Parameters:

arg0 - the key

arg1 - the values

arg2 - collects mapped keys and values

Throws:

IOException