Uses of Class

Packages that use Reducer
org.apache.hadoop.examples Hadoop example code. 
org.apache.hadoop.mapred A software framework for easily writing applications which process vast amounts of data (multi-terabyte data-sets) parallelly on large clusters (thousands of nodes) built of commodity hardware in a reliable, fault-tolerant manner. 

Uses of Reducer in org.apache.hadoop.examples

Subclasses of Reducer in org.apache.hadoop.examples
static class SecondarySort.Reduce
          A reducer class that just emits the sum of the input values.
static class WordCount.IntSumReducer

Uses of Reducer in org.apache.hadoop.mapred

Methods in org.apache.hadoop.mapred with parameters of type Reducer
protected static
Task.createReduceContext(Reducer<INKEY,INVALUE,OUTKEY,OUTVALUE> reducer, Configuration job, TaskAttemptID taskId, RawKeyValueIterator rIter, Counter inputKeyCounter, Counter inputValueCounter, RecordWriter<OUTKEY,OUTVALUE> output, OutputCommitter committer, StatusReporter reporter, RawComparator<INKEY> comparator, Class<INKEY> keyClass, Class<INVALUE> valueClass)

Uses of Reducer in org.apache.hadoop.mapreduce

Methods in org.apache.hadoop.mapreduce that return types with arguments of type Reducer
 Class<? extends Reducer<?,?,?,?>> JobContext.getCombinerClass()
          Get the combiner class for the job.
 Class<? extends Reducer<?,?,?,?>> JobContext.getReducerClass()
          Get the Reducer class for the job.

Method parameters in org.apache.hadoop.mapreduce with type arguments of type Reducer
 void Job.setCombinerClass(Class<? extends Reducer> cls)
          Set the combiner class for the job.
 void Job.setReducerClass(Class<? extends Reducer> cls)
          Set the Reducer for the job.

Uses of Reducer in org.apache.hadoop.mapreduce.lib.fieldsel

Subclasses of Reducer in org.apache.hadoop.mapreduce.lib.fieldsel
 class FieldSelectionReducer<K,V>
          This class implements a reducer class that can be used to perform field selections in a manner similar to unix cut.

Uses of Reducer in org.apache.hadoop.mapreduce.lib.reduce

Subclasses of Reducer in org.apache.hadoop.mapreduce.lib.reduce
 class IntSumReducer<Key>
 class LongSumReducer<KEY>

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