package de.lmu.ifi.dbs.elki.datasource.filter;
/*
This file is part of ELKI:
Environment for Developing KDD-Applications Supported by Index-Structures
Copyright (C) 2012
Ludwig-Maximilians-Universität München
Lehr- und Forschungseinheit für Datenbanksysteme
ELKI Development Team
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/>.
*/
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import de.lmu.ifi.dbs.elki.datasource.bundle.MultipleObjectsBundle;
import de.lmu.ifi.dbs.elki.logging.Logging;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.AbstractParameterizer;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.OptionID;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.parameterization.Parameterization;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.parameters.LongParameter;
/**
* A filter to shuffle the dataset.
*
* @author Erich Schubert
*/
public class ShuffleObjectsFilter implements ObjectFilter {
/**
* Class logger
*/
private static final Logging logger = Logging.getLogger(ShuffleObjectsFilter.class);
/**
* Optional parameter to specify a seed for randomly shuffling the rows of the
* database. If unused, no shuffling will be performed. Shuffling takes time
* linearly dependent from the size of the database.
* <p>
* Key: {@code -dbc.seed}
* </p>
*/
public static final OptionID SEED_ID = OptionID.getOrCreateOptionID("dbc.seed", "Seed for randomly shuffling the rows for the database. If the parameter is not set, no shuffling will be performed.");
/**
* Seed for randomly shuffling the rows of the database. If null, no shuffling
* will be performed. Shuffling takes time linearly dependent from the size of
* the database.
*/
final Long seed;
/**
* Constructor.
*
* @param seed Seed value, may be {@code null} for a random seed.
*/
public ShuffleObjectsFilter(Long seed) {
super();
this.seed = seed;
}
@Override
public MultipleObjectsBundle filter(MultipleObjectsBundle objects) {
if(logger.isDebugging()) {
logger.debug("Shuffling the data set");
}
final Random random = (seed == null) ? new Random() : new Random(seed);
final int size = objects.dataLength();
final int[] offsets = new int[size];
for(int i = 0; i < size; i++) {
offsets[i] = i;
}
// Randomize the offset array
for(int i = size; i > 1; i--) {
final int j = random.nextInt(i);
// Swap the elements at positions j and i - 1:
final int temp = offsets[j];
offsets[j] = offsets[i - 1];
offsets[i - 1] = temp;
}
MultipleObjectsBundle bundle = new MultipleObjectsBundle();
for(int j = 0; j < objects.metaLength(); j++) {
// Reorder column accordingly
List<?> in = objects.getColumn(j);
List<Object> data = new ArrayList<Object>(size);
for(int i = 0; i < size; i++) {
data.add(in.get(offsets[i]));
}
bundle.appendColumn(objects.meta(j), data);
}
return bundle;
}
/**
* Parameterization class.
*
* @author Erich Schubert
*
* @apiviz.exclude
*/
public static class Parameterizer extends AbstractParameterizer {
Long seed = null;
@Override
protected void makeOptions(Parameterization config) {
super.makeOptions(config);
LongParameter seedParam = new LongParameter(SEED_ID, true);
if(config.grab(seedParam)) {
seed = seedParam.getValue();
}
}
@Override
protected Object makeInstance() {
return new ShuffleObjectsFilter(seed);
}
}
}