rank-feature-extractor.H

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#ifndef RERANKER_RANK_FEATURE_EXTRACTOR_H_
#define RERANKER_RANK_FEATURE_EXTRACTOR_H_

#include <cmath>
#include <sstream>

#include "feature-extractor.H"

namespace reranker {

using std::stringstream;

class RankFeatureExtractor : public FeatureExtractor {
 public:
  RankFeatureExtractor() : FeatureExtractor() {
  }
  virtual ~RankFeatureExtractor() { }

  virtual void RegisterInitializers(Initializers &initializers) {
    initializers.Add("add_score_factor", &add_score_factor_);
    initializers.Add("add_score_difference", &add_score_difference_);
  }

  virtual void Extract(Candidate &candidate,
                       FeatureVector<int,double> &features) { }

  virtual void ExtractSymbolic(Candidate &candidate,
                               FeatureVector<string,double> &symbolic_features)
  {
    stringstream ss;
    ss << "orig_rank:" << candidate.index();
    symbolic_features.IncrementWeight(ss.str(), 1.0);

    stringstream lg_rank_ss;
    double lg_rank = floor(log((double)candidate.index() + 1.0) /
                           log(2.0) + 0.5);
    lg_rank_ss << "lg_rank:" << lg_rank;
    symbolic_features.IncrementWeight(lg_rank_ss.str(), 1.0);

    if (add_score_factor_) {
      double top_baseline_score =
          top_baseline_score_ == 0.0 ? 1e-10 : top_baseline_score_;
      double score_factor = candidate.baseline_score() / top_baseline_score;
      symbolic_features.IncrementWeight("score_factor", score_factor);
    }
    if (add_score_difference_) {
      double score_difference =
          candidate.baseline_score() - top_baseline_score_;
      symbolic_features.IncrementWeight("score_difference", score_difference);
    }
  }

  virtual void Extract(CandidateSet &candidate_set) {
    top_baseline_score_ = candidate_set.Get(0).baseline_score();
    FeatureExtractor::Extract(candidate_set);
  }

 private:
  double top_baseline_score_;
  bool add_score_factor_;
  bool add_score_difference_;
};

}  // namespace reranker

#endif