code: public String getCategoryName(int i )
      {
          if(i < getNumCategoricalVars() && i >= 0)
              return categories[i].getCategoryName();
          else
              throw new IndexOutOfBoundsException("Can not acces variable for invalid index  " + i );
      }
docs: Returns the name used for the <tt>i</tt>'th categorical attribute.
  @param i the <tt>i</tt>th attribute.
  @return the name used for the <tt>i</tt>'th categorical attribute.