org.jaitools.numeric
Class ApproxMedianProcessor

java.lang.Object
  org.jaitools.numeric.AbstractProcessor
      org.jaitools.numeric.ApproxMedianProcessor

All Implemented Interfaces:

Processor

public class ApproxMedianProcessor
extends AbstractProcessor

Processor for the approximate median Statistic.APPROX_MEDIAN. Calculation of an exact median is only possible by storing all sample values. For very large data streams, this processor will calculate an approximate median using the remedian estimator:

PJ Rousseeuw and GW Bassett (1990) The remedian: a robust averaging method for large data sets. Journal of the American Statistical Society 85:97-104

The remedian estimator performs badly with non-stationary data, e.g. a data stream that is monotonically increasing will result in an over-estimate. If possible (which it probably isn't), it will help to de-trend or randomly order the data prior to streaming it.

Since:

1.0

Version:

$Id$

Author:

Michael Bedward

See Also:

Statistic, StreamingSampleStats

Field Summary

Fields inherited from class org.jaitools.numeric.AbstractProcessor

numAccepted, numNaN, numNoData, numOffered

Constructor Summary

ApproxMedianProcessor()
Default constructor.

Method Summary

Double	get(Statistic stat) Gets the value of the statistic calculated by this processor.
Collection<Statistic>	getSupported() Gets the Statistics supported by this processor.
protected boolean	update(Double sample) Processes a sample value.

Methods inherited from class org.jaitools.numeric.AbstractProcessor

addNoDataRange, addNoDataValue, addRange, addRange, get, getNoDataRanges, getNumAccepted, getNumNaN, getNumNoData, getNumOffered, getRanges, getRangesType, isAccepted, offer, setRangesType

Methods inherited from class java.lang.Object

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

Constructor Detail

ApproxMedianProcessor

public ApproxMedianProcessor()

Default constructor.

Method Detail

getSupported

public Collection<Statistic> getSupported()

Gets the Statistics supported by this processor.

Returns:

supported Statistics

update

protected boolean update(Double sample)

Processes a sample value.

Specified by:

update in class AbstractProcessor

Parameters:

sample - the sample value

Returns:

true if the sample is accepted; false otherwise

get

public Double get(Statistic stat)

Gets the value of the statistic calculated by this processor.

Parameters:

stat - the specified statistic

Returns:

the value of the statistic if it has been calculated or Double.NaN otherwise