code: def get_tiered_meth_category(self, mtype, all_codes, code_types):
          
          categories = Series(code_types[code_types[mtype] == True].index)
          codes = {cat: list(self.get_one_meth_type(cat, all_codes).index) for cat in categories}
          return codes
docs: Get a tiered list of all er/pmag_age codes
          i.e. pmag_codes = {'anisotropy_codes': ['code1', 'code2'],
          'sample_preparation': [code1, code2], ...}