std::vector<double> get_associations(const std::vector<Page>& pages,
				     const std::vector<Word>& words,
				     const std::vector<std::string>& keywords,
				     const bool normalizable) {
  std::map<int, int> pid_conv;
  for(int i = 0; i < static_cast<int>(pages.size()); ++i) {
    pid_conv[pages[i].id()] = i;
  }

  std::map<std::string, int> word_conv;
  for(int i = 0; i < static_cast<int>(words.size()); ++i) {
    word_conv[words[i].str()] = i;
  }

  std::vector<double> associations(pages.size(), 0.0);
  for(const std::string& keyword : keywords) {
    if(!word_conv.count(keyword)) continue;
    int widx = word_conv[keyword];
    std::set<int> pid_set;
    for(const auto& location : words[widx].locations()) {
      pid_set.insert(location.first);
    }
    for(int pid : pid_set) {
      if(pid_conv.count(pid)) associations[pid_conv[pid]] += 1.0;
    }
  }

  if(normalizable) {
    double max_association = *std::max_element(associations.begin(), associations.end());
    if(max_association != 0.0) {
      for(int i = 0; i < static_cast<int>(pages.size()); ++i) {
	associations[i] /= max_association;
      }
    }
  }

  return associations;
}