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package de.lmu.ifi.dbs.elki.evaluation.scores;
/*
This file is part of ELKI:
Environment for Developing KDD-Applications Supported by Index-Structures
Copyright (C) 2015
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 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.constraints.CommonConstraints;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.parameterization.Parameterization;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.parameters.IntParameter;
/**
* Evaluate using Precision@k, or R-precision (when {@code k=0}).
*
* When {@code k=0}, then it is set to the number of positive objects, and the
* returned value is the R-precision, or the precision-recall break-even-point
* (BEP).
*
* @author Erich Schubert
*/
public class PrecisionAtKEvaluation extends AbstractScoreEvaluation {
/**
* Static instance
*/
public static final PrecisionAtKEvaluation RPRECISION = new PrecisionAtKEvaluation(0);
/**
* Parameter k.
*/
int k;
/**
* Constructor.
*
* @param k k to evaluate at. May be 0.
*/
public PrecisionAtKEvaluation(int k) {
this.k = k;
}
@Override
public <I extends ScoreIter> double evaluate(Predicate<? super I> predicate, I iter) {
final int k = (this.k > 0) ? this.k : predicate.numPositive();
int total = 0;
double score = 0.;
while(iter.valid() && total < k) {
int posthis = 0, cntthis = 0;
// positive or negative match?
do {
if(predicate.test(iter)) {
++posthis;
}
++cntthis;
iter.advance();
} // Loop while tied:
while(iter.valid() && iter.tiedToPrevious());
// Special tie computations only when we reach k.
if(total + cntthis > k) {
// p = posthis / cntthis chance of being positive
// n = (k-total) draws.
// expected value = n * p
score += posthis / (double) cntthis * (k - total);
total = k;
break;
}
score += posthis;
total += cntthis;
}
return score / total;
}
@Override
public double expected(int pos, int all) {
return pos / (double) all;
}
/**
* Parameterization class.
*
* @author Erich Schubert
*
* @apiviz.exclude
*/
public static class Parameterizer extends AbstractParameterizer {
/**
* Option ID for the k parameter.
*/
public static final OptionID K_ID = new OptionID("precision.k", //
"k value for precision@k. Can be set to 0, to get R-precision, or the precision-recall-break-even-point.");
/**
* K parameter
*/
int k;
@Override
protected void makeOptions(Parameterization config) {
super.makeOptions(config);
IntParameter kP = new IntParameter(K_ID) //
.setDefaultValue(0) //
.addConstraint(CommonConstraints.GREATER_EQUAL_ZERO_INT);
if(config.grab(kP)) {
k = kP.intValue();
}
}
@Override
protected PrecisionAtKEvaluation makeInstance() {
return k > 0 ? new PrecisionAtKEvaluation(k) : RPRECISION;
}
}
}
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