/*
 *  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.example.set;

import java.util.Random;

import com.rapidminer.tools.RandomGenerator;


/**
 * Creates a shuffled partition for an example set. This implementation traverses 
 * the partition backwards, from the last element up to the second, repeatedly 
 * swapping a randomly selected element into the "current position". Elements 
 * are randomly selected from the portion of the list that runs from the first 
 * element to the current position, inclusive.
 * 
 * @author Ingo Mierswa
 */
public class ShuffledPartitionBuilder extends SimplePartitionBuilder {

	private Random random;

	public ShuffledPartitionBuilder(boolean useLocalRandomSeed, int seed) {
		this.random = RandomGenerator.getRandomGenerator(useLocalRandomSeed, seed);
	}

	/**
	 * Returns a shuffled partition for an example set. Uses the partition
	 * delivered by the superclass and shuffles the elements.
	 */
	@Override
	public int[] createPartition(double[] ratio, int size) {
		int[] part = super.createPartition(ratio, size);

		// Create a random permutation of the generated array by swapping
		// elements
		for (int i = part.length - 1; i >= 1; i--) {
			int swap = random.nextInt(i);
			int dummy = part[i];
			part[i] = part[swap];
			part[swap] = dummy;
		}

		return part;
	}
}
