ngram-feature-extractor.H

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#ifndef RERANKER_NGRAM_FEATURE_EXTRACTOR_H_
#define RERANKER_NGRAM_FEATURE_EXTRACTOR_H_

#include <sstream>
#include <cstdlib>
#include <string>
#include <vector>

#include "feature-extractor.H"
#include "tokenizer.H"

namespace reranker {

using std::string;
using std::stringstream;
using std::vector;

class NgramExtractor {
 public:
  void Extract(const vector<string> &tokens,
               const int n,
               const string &prefix,
               FeatureVector<string,double> &symbolic_features) const;
};

class NgramFeatureExtractor : public FeatureExtractor {
 public:
  NgramFeatureExtractor() : FeatureExtractor(), prefix_("") { }
  virtual ~NgramFeatureExtractor() { }

  virtual void RegisterInitializers(Initializers &initializers) {
    bool required = true;
    initializers.Add("n", &n_, required);
    initializers.Add("prefix", &prefix_);
  }

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

  virtual void ExtractSymbolic(Candidate &candidate,
                               FeatureVector<string,double> &symbolic_features);
 private:
  // data members
  int n_;
  string prefix_;
  NgramExtractor ngram_extractor_;
  Tokenizer tokenizer_;
};

}  // namespace reranker

#endif