/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/*
* CorrelationSplitInfo.java
* Copyright (C) 2000 University of Waikato, Hamilton, New Zealand
*
*/
package weka.classifiers.trees.m5;
import weka.core.Instances;
import weka.core.RevisionHandler;
import weka.core.RevisionUtils;
import weka.core.Utils;
import weka.experiment.PairedStats;
import java.io.Serializable;
/**
* Finds split points using correlation.
*
* @author Mark Hall (mhall@cs.waikato.ac.nz)
* @version $Revision: 1.4 $
*/
public final class CorrelationSplitInfo
implements Cloneable, Serializable, SplitEvaluate, RevisionHandler {
/** for serialization */
private static final long serialVersionUID = 4212734895125452770L;
/**
* the first instance
*/
private int m_first;
/**
* the last instance
*/
private int m_last;
private int m_position;
/**
* the maximum impurity reduction
*/
private double m_maxImpurity;
/**
* the attribute being tested
*/
private int m_splitAttr;
/**
* the best value on which to split
*/
private double m_splitValue;
/**
* the number of instances
*/
private int m_number;
/**
* Constructs an object which contains the split information
*
* @param low the index of the first instance
* @param high the index of the last instance
* @param attr an attribute
*/
public CorrelationSplitInfo(int low, int high, int attr) {
initialize(low, high, attr);
}
/**
* Makes a copy of this CorrelationSplitInfo object
*/
public final SplitEvaluate copy() throws Exception {
CorrelationSplitInfo s = (CorrelationSplitInfo) this.clone();
return s;
}
/**
* Resets the object of split information
*
* @param low the index of the first instance
* @param high the index of the last instance
* @param attr the attribute
*/
public final void initialize(int low, int high, int attr) {
m_number = high - low + 1;
m_first = low;
m_last = high;
m_position = -1;
m_maxImpurity = -Double.MAX_VALUE;
m_splitAttr = attr;
m_splitValue = 0.0;
}
/**
* Finds the best splitting point for an attribute in the instances
*
* @param attr the splitting attribute
* @param inst the instances
* @exception Exception if something goes wrong
*/
public final void attrSplit(int attr, Instances inst) throws Exception {
int i;
int len;
int part;
int low = 0;
int high = inst.numInstances() - 1;
PairedStats full = new PairedStats(0.01);
PairedStats leftSubset = new PairedStats(0.01);
PairedStats rightSubset = new PairedStats(0.01);
int classIndex = inst.classIndex();
double leftCorr, rightCorr;
double leftVar, rightVar, allVar;
double order = 2.0;
initialize(low, high, attr);
if (m_number < 4) {
return;
}
len = ((high - low + 1) < 5) ? 1 : (high - low + 1) / 5;
m_position = low;
part = low + len - 1;
// prime the subsets
for (i = low; i < len; i++) {
full.add(inst.instance(i).value(attr),
inst.instance(i).value(classIndex));
leftSubset.add(inst.instance(i).value(attr),
inst.instance(i).value(classIndex));
}
for (i = len; i < inst.numInstances(); i++) {
full.add(inst.instance(i).value(attr),
inst.instance(i).value(classIndex));
rightSubset.add(inst.instance(i).value(attr),
inst.instance(i).value(classIndex));
}
full.calculateDerived();
allVar = (full.yStats.stdDev * full.yStats.stdDev);
allVar = Math.abs(allVar);
allVar = Math.pow(allVar, (1.0 / order));
for (i = low + len; i < high - len - 1; i++) {
rightSubset.subtract(inst.instance(i).value(attr),
inst.instance(i).value(classIndex));
leftSubset.add(inst.instance(i).value(attr),
inst.instance(i).value(classIndex));
if (!Utils.eq(inst.instance(i + 1).value(attr),
inst.instance(i).value(attr))) {
leftSubset.calculateDerived();
rightSubset.calculateDerived();
leftCorr = Math.abs(leftSubset.correlation);
rightCorr = Math.abs(rightSubset.correlation);
leftVar = (leftSubset.yStats.stdDev * leftSubset.yStats.stdDev);
leftVar = Math.abs(leftVar);
leftVar = Math.pow(leftVar, (1.0 / order));
rightVar = (rightSubset.yStats.stdDev * rightSubset.yStats.stdDev);
rightVar = Math.abs(rightVar);
rightVar = Math.pow(rightVar, (1.0 / order));
double score = allVar - ((leftSubset.count / full.count) * leftVar)
- ((rightSubset.count / full.count) * rightVar);
// score /= allVar;
leftCorr = (leftSubset.count / full.count) * leftCorr;
rightCorr = (rightSubset.count / full.count) * rightCorr;
double c_score = (leftCorr + rightCorr) - Math.abs(full.correlation);
// c_score += score;
if (!Utils.eq(score, 0.0)) {
if (score > m_maxImpurity) {
m_maxImpurity = score;
m_splitValue =
(inst.instance(i).value(attr) + inst.instance(i + 1)
.value(attr)) * 0.5;
m_position = i;
}
}
}
}
}
/**
* Returns the impurity of this split
*
* @return the impurity of this split
*/
public double maxImpurity() {
return m_maxImpurity;
}
/**
* Returns the attribute used in this split
*
* @return the attribute used in this split
*/
public int splitAttr() {
return m_splitAttr;
}
/**
* Returns the position of the split in the sorted values. -1 indicates that
* a split could not be found.
*
* @return an <code>int</code> value
*/
public int position() {
return m_position;
}
/**
* Returns the split value
*
* @return the split value
*/
public double splitValue() {
return m_splitValue;
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 1.4 $");
}
}