/*
* 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.
*/
/*
* ZeroR.java
* Copyright (C) 1999 University of Waikato, Hamilton, New Zealand
*
*/
package weka.classifiers.rules;
import weka.classifiers.Classifier;
import weka.classifiers.Sourcable;
import weka.core.Attribute;
import weka.core.Capabilities;
import weka.core.Instance;
import weka.core.Instances;
import weka.core.RevisionUtils;
import weka.core.Utils;
import weka.core.WeightedInstancesHandler;
import weka.core.Capabilities.Capability;
import java.util.Enumeration;
/**
<!-- globalinfo-start -->
* Class for building and using a 0-R classifier. Predicts the mean (for a numeric class) or the mode (for a nominal class).
* <p/>
<!-- globalinfo-end -->
*
<!-- options-start -->
* Valid options are: <p/>
*
* <pre> -D
* If set, classifier is run in debug mode and
* may output additional info to the console</pre>
*
<!-- options-end -->
*
* @author Eibe Frank (eibe@cs.waikato.ac.nz)
* @version $Revision: 1.19 $
*/
public class ZeroR
extends Classifier
implements WeightedInstancesHandler, Sourcable {
/** for serialization */
static final long serialVersionUID = 48055541465867954L;
/** The class value 0R predicts. */
private double m_ClassValue;
/** The number of instances in each class (null if class numeric). */
private double [] m_Counts;
/** The class attribute. */
private Attribute m_Class;
/**
* 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 0-R classifier. Predicts the mean "
+ "(for a numeric class) or the mode (for a nominal class).";
}
/**
* Returns default capabilities of the classifier.
*
* @return the capabilities of this classifier
*/
public Capabilities getCapabilities() {
Capabilities result = super.getCapabilities();
// attributes
result.enable(Capability.NOMINAL_ATTRIBUTES);
result.enable(Capability.NUMERIC_ATTRIBUTES);
result.enable(Capability.DATE_ATTRIBUTES);
result.enable(Capability.STRING_ATTRIBUTES);
result.enable(Capability.RELATIONAL_ATTRIBUTES);
result.enable(Capability.MISSING_VALUES);
// class
result.enable(Capability.NOMINAL_CLASS);
result.enable(Capability.NUMERIC_CLASS);
result.enable(Capability.DATE_CLASS);
result.enable(Capability.MISSING_CLASS_VALUES);
// instances
result.setMinimumNumberInstances(0);
return result;
}
/**
* Generates the classifier.
*
* @param instances set of instances serving as training data
* @throws Exception if the classifier has not been generated successfully
*/
public void buildClassifier(Instances instances) throws Exception {
// can classifier handle the data?
getCapabilities().testWithFail(instances);
// remove instances with missing class
instances = new Instances(instances);
instances.deleteWithMissingClass();
double sumOfWeights = 0;
m_Class = instances.classAttribute();
m_ClassValue = 0;
switch (instances.classAttribute().type()) {
case Attribute.NUMERIC:
m_Counts = null;
break;
case Attribute.NOMINAL:
m_Counts = new double [instances.numClasses()];
for (int i = 0; i < m_Counts.length; i++) {
m_Counts[i] = 1;
}
sumOfWeights = instances.numClasses();
break;
}
Enumeration enu = instances.enumerateInstances();
while (enu.hasMoreElements()) {
Instance instance = (Instance) enu.nextElement();
if (!instance.classIsMissing()) {
if (instances.classAttribute().isNominal()) {
m_Counts[(int)instance.classValue()] += instance.weight();
} else {
m_ClassValue += instance.weight() * instance.classValue();
}
sumOfWeights += instance.weight();
}
}
if (instances.classAttribute().isNumeric()) {
if (Utils.gr(sumOfWeights, 0)) {
m_ClassValue /= sumOfWeights;
}
} else {
m_ClassValue = Utils.maxIndex(m_Counts);
Utils.normalize(m_Counts, sumOfWeights);
}
}
/**
* Classifies a given instance.
*
* @param instance the instance to be classified
* @return index of the predicted class
*/
public double classifyInstance(Instance instance) {
return m_ClassValue;
}
/**
* Calculates the class membership probabilities for the given test instance.
*
* @param instance the instance to be classified
* @return predicted class probability distribution
* @throws Exception if class is numeric
*/
public double [] distributionForInstance(Instance instance)
throws Exception {
if (m_Counts == null) {
double[] result = new double[1];
result[0] = m_ClassValue;
return result;
} else {
return (double []) m_Counts.clone();
}
}
/**
* Returns a string that describes the classifier as source. The
* classifier will be contained in a class with the given name (there may
* be auxiliary classes),
* and will contain a method with the signature:
* <pre><code>
* public static double classify(Object[] i);
* </code></pre>
* where the array <code>i</code> contains elements that are either
* Double, String, with missing values represented as null. The generated
* code is public domain and comes with no warranty.
*
* @param className the name that should be given to the source class.
* @return the object source described by a string
* @throws Exception if the souce can't be computed
*/
public String toSource(String className) throws Exception {
StringBuffer result;
result = new StringBuffer();
result.append("class " + className + " {\n");
result.append(" public static double classify(Object[] i) {\n");
if (m_Counts != null)
result.append(" // always predicts label '" + m_Class.value((int) m_ClassValue) + "'\n");
result.append(" return " + m_ClassValue + ";\n");
result.append(" }\n");
result.append("}\n");
return result.toString();
}
/**
* Returns a description of the classifier.
*
* @return a description of the classifier as a string.
*/
public String toString() {
if (m_Class == null) {
return "ZeroR: No model built yet.";
}
if (m_Counts == null) {
return "ZeroR predicts class value: " + m_ClassValue;
} else {
return "ZeroR predicts class value: " + m_Class.value((int) m_ClassValue);
}
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 1.19 $");
}
/**
* Main method for testing this class.
*
* @param argv the options
*/
public static void main(String [] argv) {
runClassifier(new ZeroR(), argv);
}
}