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## org.apache.hadoop.mapred.lib.aggregate
Class ValueHistogram

    java.lang.Object
      org.apache.hadoop.mapred.lib.aggregate.ValueHistogram

All Implemented Interfaces:
  ValueAggregator

    public class ValueHistogram

extends Object
implements ValueAggregator

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

Constructor Summary
`ValueHistogram()`

Method Summary
`void` | `addNextValue(Object val)` add the given val to the aggregator.
`ArrayList` | `getCombinerOutput()`
`String` | `getReport()`
`String` | `getReportDetails()`
`TreeMap` | `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 Detail

### ValueHistogram

    public ValueHistogram()

Method Detail

### addNextValue

    public void addNextValue(Object val)

  add the given val to the aggregator.

  Specified by:
    `addNextValue` in interface `ValueAggregator`
  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`
  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 getCombinerOutput()

  Specified by:
    `getCombinerOutput` in interface `ValueAggregator`
  Returns:
    a list value/frequence pairs. The return value is expected to be used by the reducer.

### getReportItems

    public TreeMap getReportItems()

  Returns:
    a TreeMap representation of the histogram

### reset

    public void reset()

  reset the aggregator

  Specified by:
    `reset` in interface `ValueAggregator`

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Copyright © 2009 The Apache Software Foundation