Package org.apache.hadoop.mapreduce.lib.aggregate

Class ValueHistogram

java.lang.Object

org.apache.hadoop.mapreduce.lib.aggregate.ValueHistogram

All Implemented Interfaces:

ValueAggregator<String>

Direct Known Subclasses:

ValueHistogram

@Public
@Stable
public class ValueHistogram
extends Object
implements ValueAggregator<String>

This class implements a value aggregator that computes the histogram of a sequence of strings.

Constructor Summary

Constructors

Constructor	Description
ValueHistogram()

Method Summary

Modifier and Type	Method	Description
void	addNextValue(Object val)	add the given val to the aggregator.
ArrayList<String>	getCombinerOutput()
String	getReport()
String	getReportDetails()
TreeMap<Object,Object>	getReportItems()
void	reset()	reset the aggregator

Methods inherited from class java.lang.Object

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

Constructor Details

ValueHistogram

public ValueHistogram()

Method Details

addNextValue

public void addNextValue(Object val)

add the given val to the aggregator.

Specified by:

addNextValue in interface ValueAggregator<String>

Parameters:

val - the value to be added. It is expected to be a string in the form of xxxx\tnum, meaning xxxx has num occurrences.

getReport

public String getReport()

Specified by:

getReport in interface ValueAggregator<String>

Returns:

the string representation of this aggregator. It includes the following basic statistics of the histogram: the number of unique values the minimum value the media value the maximum value the average value the standard deviation

getReportDetails

public String getReportDetails()

Returns:

a string representation of the list of value/frequence pairs of the histogram

getCombinerOutput

public ArrayList<String> getCombinerOutput()

Specified by:

getCombinerOutput in interface ValueAggregator<String>

Returns:

a list value/frequence pairs. The return value is expected to be used by the reducer.

getReportItems

public TreeMap<Object,Object> getReportItems()

Returns:

a TreeMap representation of the histogram

reset

public void reset()

reset the aggregator

Specified by:

reset in interface ValueAggregator<String>