samoa-api/src/main/java/org/apache/samoa/moa/classifiers/functions/MajorityClass.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.samoa.moa.classifiers.functions;

import org.apache.samoa.instances.Instance;
import org.apache.samoa.moa.classifiers.AbstractClassifier;
import org.apache.samoa.moa.core.DoubleVector;
import org.apache.samoa.moa.core.Measurement;
import org.apache.samoa.moa.core.StringUtils;

/**
 * Majority class learner. This is the simplest classifier.
 * 
 * @author Richard Kirkby (rkirkby@cs.waikato.ac.nz)
 * @version $Revision: 7 $
 */
public class MajorityClass extends AbstractClassifier {

  private static final long serialVersionUID = 1L;

  @Override
  public String getPurposeString() {
    return "Majority class classifier: always predicts the class that has been observed most frequently the in the training data.";
  }

  protected DoubleVector observedClassDistribution;

  @Override
  public void resetLearningImpl() {
    this.observedClassDistribution = new DoubleVector();
  }

  @Override
  public void trainOnInstanceImpl(Instance inst) {
    this.observedClassDistribution.addToValue((int) inst.classValue(), inst.weight());
  }

  public double[] getVotesForInstance(Instance i) {
    return this.observedClassDistribution.getArrayCopy();
  }

  @Override
  protected Measurement[] getModelMeasurementsImpl() {
    return null;
  }

  @Override
  public void getModelDescription(StringBuilder out, int indent) {
    StringUtils.appendIndented(out, indent, "Predicted majority ");
    out.append(getClassNameString());
    out.append(" = ");
    out.append(getClassLabelString(this.observedClassDistribution.maxIndex()));
    StringUtils.appendNewline(out);
    for (int i = 0; i < this.observedClassDistribution.numValues(); i++) {
      StringUtils.appendIndented(out, indent, "Observed weight of ");
      out.append(getClassLabelString(i));
      out.append(": ");
      out.append(this.observedClassDistribution.getValue(i));
      StringUtils.appendNewline(out);
    }
  }

  public boolean isRandomizable() {
    return false;
  }
}