samoa-api/src/main/java/org/apache/samoa/moa/classifiers/rules/core/voting/InverseErrorWeightedVote.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.rules.core.voting;

/**
 * InverseErrorWeightedVote class for weighted votes based on estimates of errors.
 * 
 * @author Joao Duarte (jmduarte@inescporto.pt)
 * @version $Revision: 1 $
 */
public class InverseErrorWeightedVote extends AbstractErrorWeightedVote {

  /**
	 * 
	 */
  private static final double EPS = 0.000000001; // just to prevent divide by 0 in 1/X -> 1/(x+EPS)
  private static final long serialVersionUID = 6359349250620616482L;

  public InverseErrorWeightedVote() {
    super();
  }

  public InverseErrorWeightedVote(AbstractErrorWeightedVote aewv) {
    super(aewv);
  }

  @Override
  public double[] computeWeightedVote() {
    int n = votes.size();
    weights = new double[n];
    double[] weightedVote = null;
    if (n > 0) {
      int d = votes.get(0).length;
      weightedVote = new double[d];
      double sumError = 0;
      // weights are 1/(error+eps)
      for (int i = 0; i < n; ++i) {
        if (errors.get(i) < Double.MAX_VALUE) {
          weights[i] = 1.0 / (errors.get(i) + EPS);
          sumError += weights[i];
        }
        else
          weights[i] = 0;

      }

      if (sumError > 0)
        for (int i = 0; i < n; ++i)
        {
          // normalize so that weights sum 1
          weights[i] /= sumError;
          // compute weighted vote
          for (int j = 0; j < d; j++)
            weightedVote[j] += votes.get(i)[j] * weights[i];
        }
      // Only occurs if all errors=Double.MAX_VALUE
      else
      {
        // compute arithmetic vote
        for (int i = 0; i < n; ++i)
        {
          for (int j = 0; j < d; j++)
            weightedVote[j] += votes.get(i)[j] / n;
        }
      }
    }
    return weightedVote;
  }

  @Override
  public void getDescription(StringBuilder sb, int indent) {
    // TODO Auto-generated method stub

  }

  @Override
  public InverseErrorWeightedVote getACopy() {
    return new InverseErrorWeightedVote(this);
  }

}