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AIMA-Java Core Algorithms from the book Artificial Intelligence a Modern Approach 3rd Ed.

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package aima.core.learning.learners;

import java.util.ArrayList;
import java.util.List;

import aima.core.learning.framework.DataSet;
import aima.core.learning.framework.Example;
import aima.core.learning.framework.Learner;
import aima.core.util.Util;

/**
 * @author Ravi Mohan
 * 
 */
public class MajorityLearner implements Learner {

	private String result;

	public void train(DataSet ds) {
		List targets = new ArrayList();
		for (Example e : ds.examples) {
			targets.add(e.targetValue());
		}
		result = Util.mode(targets);
	}

	public String predict(Example e) {
		return result;
	}

	public int[] test(DataSet ds) {
		int[] results = new int[] { 0, 0 };

		for (Example e : ds.examples) {
			if (e.targetValue().equals(result)) {
				results[0] = results[0] + 1;
			} else {
				results[1] = results[1] + 1;
			}
		}
		return results;
	}
}