docs: public static List<String> inferCategories(RecordReader recordReader,int columnIndex) {
          Set<String> categories = new HashSet<>();
          while(recordReader.hasNext()) {
              List<Writable> next = recordReader.next();
              categories.add(next.get(columnIndex).toString());
          }
  
          //Sort categories alphabetically - HashSet and RecordReader orders are not deterministic in general
          List<String> ret = new ArrayList<>(categories);
          Collections.sort(ret);
          return ret;
      }