ValueAggregatorMapper (Hadoop 1.2.1 API)
Date: 2013-07-22

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## org.apache.hadoop.mapred.lib.aggregate
Class ValueAggregatorMapper<K1 extends WritableComparable,V1 extends Writable>

    java.lang.Object
      org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorJobBase<K1,V1>
          org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorMapper<K1,V1>

All Implemented Interfaces:
  Closeable, JobConfigurable, Mapper<K1,V1,Text,Text>, Reducer<Text,Text,Text,Text>

    public class ValueAggregatorMapper<K1 extends WritableComparable,V1 extends Writable>

extends ValueAggregatorJobBase<K1,V1>

This class implements the generic mapper of Aggregate.

Field Summary

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

Constructor Summary
`ValueAggregatorMapper()`

Method Summary
`void` | `map(K1 key, V1 value, OutputCollector<Text,Text> output, Reporter reporter)` the map function.
`void` | `reduce(Text arg0, Iterator<Text> arg1, OutputCollector<Text,Text> arg2, Reporter arg3)` Do nothing.

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

### ValueAggregatorMapper

    public ValueAggregatorMapper()

Method Detail

### map

    public void map(K1 key,
                    V1 value,
                    OutputCollector<Text,Text> output,
                    Reporter reporter)
             throws IOException

  the map function. It iterates through the value aggregator descriptor list to generate aggregation id/value pairs and emit them.

  Parameters:
    `key` - the input key.
    `value` - the input value.
    `output` - collects mapped keys and values.
    `reporter` - facility to report progress.
  Throws:
    `IOException`

### reduce

    public void reduce(Text arg0,
                       Iterator<Text> arg1,
                       OutputCollector<Text,Text> arg2,
                       Reporter arg3)
                throws IOException

  Do nothing. Should not be called.

  Parameters:
    `arg0` - the key.
    `arg1` - the list of values to reduce.
    `arg2` - to collect keys and combined values.
    `arg3` - facility to report progress.
  Throws:
    `IOException`

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