xapian-letor/scorer/ndcg_score.cc

   1 /** @file ndcg_score.cc
   2  *  @brief Implementation of NDCGScore
   3  */
   4 /* Copyright (C) 2014 Hanxiao Sun
   5  * Copyright (C) 2016 Ayush Tomar
   6  *
   7  * This program is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU General Public License as
   9  * published by the Free Software Foundation; either version 2 of the
  10  * License, or (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
  20  * USA
  21  */
  22
  23 #include <config.h>
  24
  25 #include "xapian-letor/scorer.h"
  26
  27 #include "debuglog.h"
  28 #include "common/log2.h"
  29
  30 #include <algorithm>
  31 #include <cmath>
  32
  33 using namespace std;
  34 using namespace Xapian;
  35
  36 NDCGScore::NDCGScore()
  37 {
  38     LOGCALL_CTOR(API, "NDCGScore", NO_ARGS);
  39 }
  40
  41 NDCGScore::~NDCGScore()
  42 {
  43     LOGCALL_DTOR(API, "NDCGScore");
  44 }
  45
  46 static double
  47 get_dcg(const std::vector<double> &labels)
  48 {
  49     LOGCALL_STATIC(API, double, "get_dcg", labels);
  50     double dcg = 0;
  51     for (int i = 0; i < int(labels.size()); ++i) {
  52         dcg += (pow(2, labels[i]) - 1) / log2(i + 2);
  53     }
  54     return dcg;
  55 }
  56
  57 double
  58 NDCGScore::score(const std::vector<FeatureVector> & fvv) const {
  59     LOGCALL(API, double, "NDCGScore::score", fvv);
  60     std::vector<double> labels;
  61     for (auto&& v : fvv) {
  62         labels.push_back(v.get_label());
  63     }
  64     // DCG score of original ranking
  65     double DCG = get_dcg(labels);
  66     // DCG score of ideal ranking
  67     sort(labels.begin(), labels.begin() + labels.size(), std::greater<double>());
  68     double iDCG = get_dcg(labels);
  69
  70     if (iDCG == 0) // Don't divide by 0
  71         return 0;
  72     return DCG / iDCG;
  73 }