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The Waikato Environment for Knowledge Analysis (WEKA), a machine
learning workbench. This is the stable version. Apart from bugfixes, this version
does not receive any other updates.
/*
* 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 3 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, see
*
* R.C. Holte (1993). Very simple classification rules perform well on most
* commonly used datasets. Machine Learning. 11:63-91.
*
*
*
* BibTeX:
*
*
* @article{Holte1993,
* author = {R.C. Holte},
* journal = {Machine Learning},
* pages = {63-91},
* title = {Very simple classification rules perform well on most commonly used datasets},
* volume = {11},
* year = {1993}
* }
*
*
*
*
* Valid options are:
*
*
*
* -B <minimum bucket size>
* The minimum number of objects in a bucket (default: 6).
*
*
*
*
* @author Ian H. Witten ([email protected])
* @version $Revision: 10153 $
*/
public class OneR extends AbstractClassifier implements
TechnicalInformationHandler, Sourcable {
/** for serialization */
static final long serialVersionUID = -3459427003147861443L;
/**
* Returns a string describing classifier
*
* @return a description suitable for displaying in the explorer/experimenter
* gui
*/
public String globalInfo() {
return "Class for building and using a 1R classifier; in other words, uses "
+ "the minimum-error attribute for prediction, discretizing numeric "
+ "attributes. For more information, see:\n\n"
+ getTechnicalInformation().toString();
}
/**
* Returns an instance of a TechnicalInformation object, containing detailed
* information about the technical background of this class, e.g., paper
* reference or book this class is based on.
*
* @return the technical information about this class
*/
@Override
public TechnicalInformation getTechnicalInformation() {
TechnicalInformation result;
result = new TechnicalInformation(Type.ARTICLE);
result.setValue(Field.AUTHOR, "R.C. Holte");
result.setValue(Field.YEAR, "1993");
result
.setValue(Field.TITLE,
"Very simple classification rules perform well on most commonly used datasets");
result.setValue(Field.JOURNAL, "Machine Learning");
result.setValue(Field.VOLUME, "11");
result.setValue(Field.PAGES, "63-91");
return result;
}
/**
* Class for storing store a 1R rule.
*/
private class OneRRule implements Serializable, RevisionHandler {
/** for serialization */
static final long serialVersionUID = 2252814630957092281L;
/** The class attribute. */
private final Attribute m_class;
/** The number of instances used for building the rule. */
private final int m_numInst;
/** Attribute to test */
private final Attribute m_attr;
/** Training set examples this rule gets right */
private int m_correct;
/** Predicted class for each value of attr */
private final int[] m_classifications;
/** Predicted class for missing values */
private int m_missingValueClass = -1;
/** Breakpoints (numeric attributes only) */
private double[] m_breakpoints;
/**
* Constructor for nominal attribute.
*
* @param data the data to work with
* @param attribute the attribute to use
* @throws Exception if something goes wrong
*/
public OneRRule(Instances data, Attribute attribute) throws Exception {
m_class = data.classAttribute();
m_numInst = data.numInstances();
m_attr = attribute;
m_correct = 0;
m_classifications = new int[m_attr.numValues()];
}
/**
* Constructor for numeric attribute.
*
* @param data the data to work with
* @param attribute the attribute to use
* @param nBreaks the break point
* @throws Exception if something goes wrong
*/
public OneRRule(Instances data, Attribute attribute, int nBreaks) throws Exception {
m_class = data.classAttribute();
m_numInst = data.numInstances();
m_attr = attribute;
m_correct = 0;
m_classifications = new int[nBreaks];
m_breakpoints = new double[nBreaks - 1]; // last breakpoint is infinity
}
/**
* Returns a description of the rule.
*
* @return a string representation of the rule
*/
@Override
public String toString() {
try {
StringBuffer text = new StringBuffer();
text.append(m_attr.name() + ":\n");
for (int v = 0; v < m_classifications.length; v++) {
text.append("\t");
if (m_attr.isNominal()) {
text.append(m_attr.value(v));
} else if (v < m_breakpoints.length) {
text.append("< " + m_breakpoints[v]);
} else if (v > 0) {
text.append(">= " + m_breakpoints[v - 1]);
} else {
text.append("not ?");
}
text.append("\t-> " + m_class.value(m_classifications[v]) + "\n");
}
if (m_missingValueClass != -1) {
text.append("\t?\t-> " + m_class.value(m_missingValueClass) + "\n");
}
text
.append("(" + m_correct + "/" + m_numInst + " instances correct)\n");
return text.toString();
} catch (Exception e) {
return "Can't print OneR classifier!";
}
}
/**
* Returns the revision string.
*
* @return the revision
*/
@Override
public String getRevision() {
return RevisionUtils.extract("$Revision: 10153 $");
}
}
/** A 1-R rule */
private OneRRule m_rule;
/** The minimum bucket size */
private int m_minBucketSize = 6;
/** a ZeroR model in case no model can be built from the data */
private Classifier m_ZeroR;
/**
* Classifies a given instance.
*
* @param inst the instance to be classified
* @return the classification of the instance
*/
@Override
public double classifyInstance(Instance inst) throws Exception {
// default model?
if (m_ZeroR != null) {
return m_ZeroR.classifyInstance(inst);
}
int v = 0;
if (inst.isMissing(m_rule.m_attr)) {
if (m_rule.m_missingValueClass != -1) {
return m_rule.m_missingValueClass;
} else {
return 0; // missing values occur in test but not training set
}
}
if (m_rule.m_attr.isNominal()) {
v = (int) inst.value(m_rule.m_attr);
} else {
while (v < m_rule.m_breakpoints.length
&& inst.value(m_rule.m_attr) >= m_rule.m_breakpoints[v]) {
v++;
}
}
return m_rule.m_classifications[v];
}
/**
* Returns default capabilities of the classifier.
*
* @return the capabilities of this classifier
*/
@Override
public Capabilities getCapabilities() {
Capabilities result = super.getCapabilities();
result.disableAll();
// attributes
result.enable(Capability.NOMINAL_ATTRIBUTES);
result.enable(Capability.NUMERIC_ATTRIBUTES);
result.enable(Capability.DATE_ATTRIBUTES);
result.enable(Capability.MISSING_VALUES);
// class
result.enable(Capability.NOMINAL_CLASS);
result.enable(Capability.MISSING_CLASS_VALUES);
return result;
}
/**
* Generates the classifier.
*
* @param instances the instances to be used for building the classifier
* @throws Exception if the classifier can't be built successfully
*/
@Override
public void buildClassifier(Instances instances) throws Exception {
boolean noRule = true;
// can classifier handle the data?
getCapabilities().testWithFail(instances);
// remove instances with missing class
Instances data = new Instances(instances);
data.deleteWithMissingClass();
// only class? -> build ZeroR model
if (data.numAttributes() == 1) {
System.err
.println("Cannot build model (only class attribute present in data!), "
+ "using ZeroR model instead!");
m_ZeroR = new weka.classifiers.rules.ZeroR();
m_ZeroR.buildClassifier(data);
return;
} else {
m_ZeroR = null;
}
// for each attribute ...
Enumeration enu = instances.enumerateAttributes();
while (enu.hasMoreElements()) {
try {
OneRRule r = newRule(enu.nextElement(), data);
// if this attribute is the best so far, replace the rule
if (noRule || r.m_correct > m_rule.m_correct) {
m_rule = r;
}
noRule = false;
} catch (Exception ex) {
}
}
if (noRule) {
throw new WekaException("No attributes found to work with!");
}
}
/**
* Create a rule branching on this attribute.
*
* @param attr the attribute to branch on
* @param data the data to be used for creating the rule
* @return the generated rule
* @throws Exception if the rule can't be built successfully
*/
public OneRRule newRule(Attribute attr, Instances data) throws Exception {
OneRRule r;
// ... create array to hold the missing value counts
int[] missingValueCounts = new int[data.classAttribute().numValues()];
if (attr.isNominal()) {
r = newNominalRule(attr, data, missingValueCounts);
} else {
r = newNumericRule(attr, data, missingValueCounts);
}
r.m_missingValueClass = Utils.maxIndex(missingValueCounts);
if (missingValueCounts[r.m_missingValueClass] == 0) {
r.m_missingValueClass = -1; // signal for no missing value class
} else {
r.m_correct += missingValueCounts[r.m_missingValueClass];
}
return r;
}
/**
* Create a rule branching on this nominal attribute.
*
* @param attr the attribute to branch on
* @param data the data to be used for creating the rule
* @param missingValueCounts to be filled in
* @return the generated rule
* @throws Exception if the rule can't be built successfully
*/
public OneRRule newNominalRule(Attribute attr, Instances data,
int[] missingValueCounts) throws Exception {
// ... create arrays to hold the counts
int[][] counts = new int[attr.numValues()][data.classAttribute()
.numValues()];
// ... calculate the counts
Enumeration enu = data.enumerateInstances();
while (enu.hasMoreElements()) {
Instance i = enu.nextElement();
if (i.isMissing(attr)) {
missingValueCounts[(int) i.classValue()]++;
} else {
counts[(int) i.value(attr)][(int) i.classValue()]++;
}
}
OneRRule r = new OneRRule(data, attr); // create a new rule
for (int value = 0; value < attr.numValues(); value++) {
int best = Utils.maxIndex(counts[value]);
r.m_classifications[value] = best;
r.m_correct += counts[value][best];
}
return r;
}
/**
* Create a rule branching on this numeric attribute
*
* @param attr the attribute to branch on
* @param data the data to be used for creating the rule
* @param missingValueCounts to be filled in
* @return the generated rule
* @throws Exception if the rule can't be built successfully
*/
public OneRRule newNumericRule(Attribute attr, Instances data,
int[] missingValueCounts) throws Exception {
// make a copy before sorting so that ties are treated consistently
// and aren't affected by sorting performed for any numeric
// attributes processed before this one
data = new Instances(data);
int lastInstance = data.numInstances();
// missing values get sorted to the end of the instances
data.sort(attr);
while (lastInstance > 0 && data.instance(lastInstance - 1).isMissing(attr)) {
lastInstance--;
missingValueCounts[(int) data.instance(lastInstance).classValue()]++;
}
if (lastInstance == 0) {
throw new Exception("Only missing values in the training data!");
}
// gather class distributions for all values
double lastValue = 0;
LinkedList distributions = new LinkedList();
LinkedList values = new LinkedList();
int[] distribution = null;
for (int i = 0; i < lastInstance; i++) {
// new value?
if ((i == 0) || (data.instance(i).value(attr) > lastValue)) {
if (i != 0) {
values.add((lastValue + data.instance(i).value(attr)) / 2.0);
}
lastValue = data.instance(i).value(attr);
distribution = new int[data.numClasses()];
distributions.add(distribution);
}
distribution[(int) data.instance(i).classValue()]++;
}
values.add(Double.MAX_VALUE);
// create iterator to go through list
ListIterator it = distributions.listIterator();
ListIterator itVals = values.listIterator();
int[] oldDist = null;
while (it.hasNext()) {
// grab next trivial bucket and iterate to next value as well
int[] newDist = it.next();
itVals.next();
// should we merge the two buckets?
if ((oldDist != null) &&
// classes the same?
((Utils.maxIndex(newDist) == Utils.maxIndex(oldDist)) ||
// bucket not large enough?
(oldDist[Utils.maxIndex(oldDist)] < m_minBucketSize))) {
// add counts
for (int j = 0; j < oldDist.length; j++) {
newDist[j] += oldDist[j];
}
// remove distribution
it.previous(); // element just visited
it.previous(); // previous element we want to remove
it.remove();
it.next(); // back to element just visited
// remove value
itVals.previous(); // element just visited
itVals.previous(); // previous element we want to remove
itVals.remove();
itVals.next(); // back to element just visited
}
// make progress
oldDist = newDist;
}
// last scan, merge adjacent intervals with same class and calculate correct
// classifications
int numCorrect = 0;
it = distributions.listIterator();
itVals = values.listIterator();
oldDist = null;
while (it.hasNext()) {
// grab next trivial bucket and iterate to next value as well
int[] newDist = it.next();
itVals.next();
// number of correct classifications does not change by merging
numCorrect += newDist[Utils.maxIndex(newDist)];
// should we merge the two buckets?
if ((oldDist != null) &&
// classes the same?
(Utils.maxIndex(newDist) == Utils.maxIndex(oldDist))) {
// add counts
for (int j = 0; j < oldDist.length; j++) {
newDist[j] += oldDist[j];
}
// remove distribution
it.previous(); // element just visited
it.previous(); // previous element we want to remove
it.remove();
it.next(); // back to element just visited
// remove value
itVals.previous(); // element just visited
itVals.previous(); // previous element we want to remove
itVals.remove();
itVals.next(); // back to element just visited
}
// make progress
oldDist = newDist;
}
OneRRule r = new OneRRule(data, attr, distributions.size()); // new rule
// with cl
// branches
r.m_correct = numCorrect;
it = distributions.listIterator();
itVals = values.listIterator();
int v = 0;
while (it.hasNext()) {
r.m_classifications[v] = Utils.maxIndex(it.next());
double splitPoint = itVals.next();
if (itVals.hasNext()) {
r.m_breakpoints[v] = splitPoint;
}
v++;
}
return r;
}
/**
* Returns an enumeration describing the available options..
*
* @return an enumeration of all the available options.
*/
@Override
public Enumeration