ciir.umass.edu.metric.ERRScorer Maven / Gradle / Ivy
/*===============================================================================
* Copyright (c) 2010-2012 University of Massachusetts. All Rights Reserved.
*
* Use of the RankLib package is subject to the terms of the software license set
* forth in the LICENSE file included with this software, and also available at
* http://people.cs.umass.edu/~vdang/ranklib_license.html
*===============================================================================
*/
package ciir.umass.edu.metric;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import ciir.umass.edu.learning.RankList;
/**
*
* @author Van Dang
* Expected Reciprocal Rank
*/
public class ERRScorer extends MetricScorer {
public static double MAX = 16;//by default, we assume the relevance scale of {0, 1, 2, 3, 4} => g_max = 4 => 2^g_max = 16
public ERRScorer() {
this.k = 10;
}
public ERRScorer(final int k) {
this.k = k;
}
@Override
public ERRScorer copy() {
return new ERRScorer();
}
/**
* Compute ERR at k. NDCG(k) = DCG(k) / DCG_{perfect}(k). Note that the "perfect ranking" must be computed based on the whole list,
* not just top-k portion of the list.
*/
@Override
public double score(final RankList rl) {
int size = k;
if (k > rl.size() || k <= 0) {
size = rl.size();
}
final List rel = new ArrayList<>();
for (int i = 0; i < rl.size(); i++) {
rel.add((int) rl.get(i).getLabel());
}
double s = 0.0;
double p = 1.0;
for (int i = 1; i <= size; i++) {
final double R = R(rel.get(i - 1));
s += p * R / i;
p *= (1.0 - R);
}
return s;
}
@Override
public String name() {
return "ERR@" + k;
}
private double R(final int rel) {
return ((1 << rel) - 1) / MAX;// (2^rel - 1)/MAX;
}
@Override
public double[][] swapChange(final RankList rl) {
final int size = (rl.size() > k) ? k : rl.size();
final int[] labels = new int[rl.size()];
final double[] R = new double[rl.size()];
final double[] np = new double[rl.size()];//p[i] = (1 - p[0])(1 - p[1])...(1-p[i-1])
double p = 1.0;
//for(int i=0;i