code: public Map<Integer, Integer> getReverseNominalMap()
      {
          Map<Integer, Integer> map = new HashMap<Integer, Integer>();
          for(int newIndex = 0; newIndex < catIndexMap.length; newIndex++)
              map.put(newIndex, catIndexMap[newIndex]);
          return map;
      }
docs: Returns a mapping from the nominal indices in the transformed space back
  to their original indices
  
  @return a mapping from the transformed nominal space to the original one