// Reduce a vector range (tally adjacent count fields of duplicate key names)
static void reduce_vec(auto& vec)  
{  
   if (vec.size() > 0) { 
      auto it1 = vec.begin(); auto itr = it1; auto itw = it1;
      auto it2 = vec.end();
      auto curr = itr;

      for (++itr; itr != it2; ++itr) {
         if (itr->first == curr->first) {
            curr->second += itr->second;
         }
         else {
            if (itw != curr)
               *itw = std::move(*curr);
            ++itw;
            curr = itr;
         }
      }

      if (itw != curr)
         *itw = std::move(*curr);
   
      vec.resize(std::distance(it1, ++itw));
   }
}