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package de.lmu.ifi.dbs.elki.index.tree.spatial.rstarvariants.strategies.bulk;
/*
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.Arrays;
import java.util.Collections;
import java.util.List;
import de.lmu.ifi.dbs.elki.data.spatial.SpatialComparable;
import de.lmu.ifi.dbs.elki.index.tree.spatial.rstarvariants.util.SpatialComparator;
import de.lmu.ifi.dbs.elki.logging.Logging;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.AbstractParameterizer;
/**
* Split strategy for bulk-loading a spatial tree where the split axes are the
* dimensions with maximum extension.
*
* @author Elke Achtert
*
* @apiviz.uses SpatialComparator
*/
public class MaxExtensionBulkSplit extends AbstractBulkSplit {
/**
* Logger.
*/
private static final Logging LOG = Logging.getLogger(MaxExtensionBulkSplit.class);
/**
* Static instance
*/
public static final MaxExtensionBulkSplit STATIC = new MaxExtensionBulkSplit();
/**
* Constructor
*/
public MaxExtensionBulkSplit() {
// Nothing to do
}
/**
* Partitions the specified feature vectors where the split axes are the
* dimensions with maximum extension.
*
* @param spatialObjects the spatial objects to be partitioned
* @param minEntries the minimum number of entries in a partition
* @param maxEntries the maximum number of entries in a partition
* @return the partition of the specified spatial objects
*/
@Override
public <N extends SpatialComparable> List<List<N>> partition(List<N> spatialObjects, int minEntries, int maxEntries) {
List<List<N>> partitions = new ArrayList<List<N>>();
List<N> objects = new ArrayList<N>(spatialObjects);
while(objects.size() > 0) {
StringBuilder msg = new StringBuilder();
// get the split axis and split point
int splitAxis = chooseMaximalExtendedSplitAxis(objects);
int splitPoint = chooseBulkSplitPoint(objects.size(), minEntries, maxEntries);
if(LOG.isDebugging()) {
msg.append("\nsplitAxis ").append(splitAxis);
msg.append("\nsplitPoint ").append(splitPoint);
}
// sort in the right dimension
Collections.sort(objects, new SpatialComparator(splitAxis, SpatialComparator.MIN));
// insert into partition
List<N> partition1 = new ArrayList<N>();
for(int i = 0; i < splitPoint; i++) {
N o = objects.remove(0);
partition1.add(o);
}
partitions.add(partition1);
// copy array
if(LOG.isDebugging()) {
msg.append("\ncurrent partition ").append(partition1);
msg.append("\nremaining objects # ").append(objects.size());
LOG.debugFine(msg.toString());
}
}
if(LOG.isDebugging()) {
LOG.debugFine("partitions " + partitions);
}
return partitions;
}
/**
* Computes and returns the best split axis. The best split axis is the split
* axes with the maximal extension.
*
* @param objects the spatial objects to be split
* @return the best split axis
*/
private int chooseMaximalExtendedSplitAxis(List<? extends SpatialComparable> objects) {
// maximum and minimum value for the extension
int dimension = objects.get(0).getDimensionality();
double[] maxExtension = new double[dimension];
double[] minExtension = new double[dimension];
Arrays.fill(minExtension, Double.MAX_VALUE);
// compute min and max value in each dimension
for(SpatialComparable object : objects) {
for(int d = 0; d < dimension; d++) {
double min, max;
min = object.getMin(d);
max = object.getMax(d);
if(maxExtension[d] < max) {
maxExtension[d] = max;
}
if(minExtension[d] > min) {
minExtension[d] = min;
}
}
}
// set split axis to dim with maximal extension
int splitAxis = -1;
double max = 0;
for(int d = 0; d < dimension; d++) {
double currentExtension = maxExtension[d] - minExtension[d];
if(max < currentExtension) {
max = currentExtension;
splitAxis = d;
}
}
return splitAxis;
}
/**
* Parameterization class.
*
* @author Erich Schubert
*
* @apiviz.exclude
*/
public static class Parameterizer extends AbstractParameterizer {
@Override
protected MaxExtensionBulkSplit makeInstance() {
return MaxExtensionBulkSplit.STATIC;
}
}
}
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