/*
 *  RapidMiner
 *
 *  Copyright (C) 2001-2011 by Rapid-I and the contributors
 *
 *  Complete list of developers available at our web site:
 *
 *       http://rapid-i.com
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Affero 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 Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public License
 *  along with this program.  If not, see http://www.gnu.org/licenses/.
 */
package com.rapidminer.operator.learner.subgroups.utility;

import com.rapidminer.operator.learner.subgroups.hypothesis.Hypothesis;
import com.rapidminer.operator.learner.subgroups.hypothesis.Rule;

/**
 * Calculates the odds ratio.
 * 
 * @author Tobias Malbrecht
 */
public class OddsRatio extends UtilityFunction {

	public OddsRatio(double totalWeight, double totalPositiveWeight) {
		super(totalWeight, totalPositiveWeight);
	}
	
	@Override
	public double utility(Rule rule) {
		double totalPredictionWeight = rule.predictsPositive() ? totalPositiveWeight : totalNegativeWeight;
		double nominator = rule.getPredictionWeight() * (totalWeight - totalPredictionWeight - rule.getCoveredWeight() + rule.getPredictionWeight());
		double denominator = (totalWeight - rule.getCoveredWeight()) * (totalWeight - totalPredictionWeight);
		return nominator / denominator;
	}
	
	@Override
	public double optimisticEstimate(Hypothesis hypothesis) {
		return Integer.MAX_VALUE;
	}

	@Override
	public String getName() {
		return "Odds Ratio";
	}
	
	@Override
	public String getAbbreviation() {
		return "OR";
	}
}