org.apache.hadoop.mapreduce.lib.aggregate
Class ValueAggregatorReducer<K1 extends org.apache.hadoop.io.WritableComparable<?>,V1 extends org.apache.hadoop.io.Writable>
java.lang.Object
org.apache.hadoop.mapreduce.Reducer<org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,org.apache.hadoop.io.Text>
org.apache.hadoop.mapreduce.lib.aggregate.ValueAggregatorReducer<K1,V1>
@InterfaceAudience.Public
@InterfaceStability.Stable
public class ValueAggregatorReducer<K1 extends org.apache.hadoop.io.WritableComparable<?>,V1 extends org.apache.hadoop.io.Writable>
- extends Reducer<org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,org.apache.hadoop.io.Text>
This class implements the generic reducer of Aggregate.
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
ValueAggregatorReducer
public ValueAggregatorReducer()
setup
public void setup(Reducer.Context context)
throws IOException,
InterruptedException
- Description copied from class:
Reducer
- Called once at the start of the task.
- Overrides:
setup
in class Reducer<org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,org.apache.hadoop.io.Text>
- Throws:
IOException
InterruptedException
reduce
public void reduce(org.apache.hadoop.io.Text key,
Iterable<org.apache.hadoop.io.Text> values,
Reducer.Context context)
throws IOException,
InterruptedException
- Description copied from class:
Reducer
- This method is called once for each key. Most applications will define
their reduce class by overriding this method. The default implementation
is an identity function.
- Overrides:
reduce
in class Reducer<org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,org.apache.hadoop.io.Text>
- 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 customized.values
- the values to be aggregatedcontext
-
- Throws:
IOException
InterruptedException
Copyright © 2012 Apache Software Foundation. All Rights Reserved.