## Package org.apache.hadoop.mapred.lib

Library of generally useful mappers, reducers, and partitioners.

See:
Description

Interface Summary
InputSampler.Sampler<K,V>: Interface to sample using an `InputFormat`.

Class Summary
ChainMapper: The ChainMapper class allows to use multiple Mapper classes within a single Map task.
ChainReducer: The ChainReducer class allows to chain multiple Mapper classes after a Reducer within the Reducer task.
CombineFileInputFormat<K,V>: An abstract `InputFormat` that returns `CombineFileSplit`'s in `InputFormat.getSplits(JobConf, int)` method.
CombineFileRecordReader<K,V>: A generic RecordReader that can hand out different recordReaders for each chunk in a `CombineFileSplit`.
CombineFileSplit: A sub-collection of input files.
DelegatingInputFormat<K,V>: An `InputFormat` that delegates behaviour of paths to multiple other InputFormats.
DelegatingMapper<K1,V1,K2,V2>: An `Mapper` that delegates behaviour of paths to multiple other mappers.
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.
HashPartitioner<K2,V2>: Partition keys by their `Object.hashCode()`.
IdentityMapper<K,V>: Implements the identity function, mapping inputs directly to outputs.
IdentityReducer<K,V>: Performs no reduction, writing all input values directly to the output.
InputSampler<K,V>: Utility for collecting samples and writing a partition file for `TotalOrderPartitioner`.
InputSampler.IntervalSampler<K,V>: Sample from s splits at regular intervals.
InputSampler.RandomSampler<K,V>: Sample from random points in the input.
InputSampler.SplitSampler<K,V>: Samples the first n records from s splits.
InverseMapper<K,V>: A `Mapper` that swaps keys and values.
KeyFieldBasedComparator<K,V>: This comparator implementation provides a subset of the features provided by the Unix/GNU Sort.
KeyFieldBasedPartitioner<K2,V2>: Defines a way to partition keys based on certain key fields (also see `KeyFieldBasedComparator`.
LongSumReducer<K>: A `Reducer` that sums long values.
MultipleInputs: This class supports MapReduce jobs that have multiple input paths with a different `InputFormat` and `Mapper` for each path
MultipleOutputFormat<K,V>: This abstract class extends the FileOutputFormat, allowing to write the output data to different output files.
MultipleOutputs: The MultipleOutputs class simplifies writting to additional outputs other than the job default output via the `OutputCollector` passed to the `map()` and `reduce()` methods of the `Mapper` and `Reducer` implementations.
MultipleSequenceFileOutputFormat<K,V>: This class extends the MultipleOutputFormat, allowing to write the output data to different output files in sequence file output format.
MultipleTextOutputFormat<K,V>: This class extends the MultipleOutputFormat, allowing to write the output data to different output files in Text output format.
MultithreadedMapRunner<K1,V1,K2,V2>: Multithreaded implementation for @link org.apache.hadoop.mapred.MapRunnable.
NLineInputFormat: NLineInputFormat which splits N lines of input as one split.
NullOutputFormat<K,V>: Consume all outputs and put them in /dev/null.
RegexMapper<K>: A `Mapper` that extracts text matching a regular expression.
TokenCountMapper<K>: A `Mapper` that maps text values into <token,freq> pairs.
TotalOrderPartitioner<K extends WritableComparable,V>: Partitioner effecting a total order by reading split points from an externally generated source.

## Package org.apache.hadoop.mapred.lib Description

Library of generally useful mappers, reducers, and partitioners.

Copyright © 2009 The Apache Software Foundation