docs: def convert_value_to_code(M_c, cidx, value):
      """
      For a column with categorical data, this function takes the raw value
      (e.g. 'Joe' or 234.23409), which is always encoded as a string, and returns the
      'code': the integer used to represent that value in the underlying representation.
  
      Note that the underlying store 'code_to_value' is unfortunately named backwards.
      TODO: fix the backwards naming.
      """
      if M_c['column_metadata'][cidx]['modeltype'] == 'normal_inverse_gamma':
          return float(value)
      else:
          return M_c['column_metadata'][cidx]['code_to_value'][str(value)]