mosesdecoder/mert/PerScorer.cpp

#include "PerScorer.h"

PerScorer::PerScorer(const string& config)
  : StatisticsBasedScorer("PER",config) {}

PerScorer::~PerScorer() {}

void PerScorer::setReferenceFiles(const vector<string>& referenceFiles)
{
  // For each line in the reference file, create a multiset of
  // the word ids.
  if (referenceFiles.size() != 1) {
    throw runtime_error("PER only supports a single reference");
  }
  _reftokens.clear();
  _reflengths.clear();
  ifstream in(referenceFiles[0].c_str());
  if (!in) {
    throw runtime_error("Unable to open " + referenceFiles[0]);
  }
  string line;
  int sid = 0;
  while (getline(in,line)) {
    vector<int> tokens;
    encode(line,tokens);
    _reftokens.push_back(multiset<int>());
    for (size_t i = 0; i < tokens.size(); ++i) {
      _reftokens.back().insert(tokens[i]);
    }
    _reflengths.push_back(tokens.size());
    if (sid > 0 && sid % 100 == 0) {
      TRACE_ERR(".");
    }
    ++sid;
  }
  TRACE_ERR(endl);

}

void PerScorer::prepareStats(size_t sid, const string& text, ScoreStats& entry)
{
  if (sid >= _reflengths.size()) {
    stringstream msg;
    msg << "Sentence id (" << sid << ") not found in reference set";
    throw runtime_error(msg.str());
  }
  // Calculate correct, output_length and ref_length for
  // the line and store it in entry
  vector<int> testtokens;
  encode(text,testtokens);
  multiset<int> testtokens_all(testtokens.begin(),testtokens.end());
  set<int> testtokens_unique(testtokens.begin(),testtokens.end());
  int correct = 0;
  for (set<int>::iterator i = testtokens_unique.begin();
       i != testtokens_unique.end(); ++i) {
    int token = *i;
    correct += min(_reftokens[sid].count(token), testtokens_all.count(token));
  }

  ostringstream stats;
  stats << correct << " " << testtokens.size() << " " << _reflengths[sid] << " " ;
  string stats_str = stats.str();
  entry.set(stats_str);
}

float PerScorer::calculateScore(const vector<int>& comps)
{
  float denom = comps[2];
  float num = comps[0] - max(0,comps[1]-comps[2]);
  if (denom == 0) {
    // This shouldn't happen!
    return 0.0;
  } else {
    return num/denom;
  }
}