def METHOD_NAME(compound_keys: pd.DataFrame) -> pd.DataFrame:
    keys = compound_keys.copy()
    mappings = {
        "fuel_agg": {
            # match values in pudl.metadata.dfs.py:EIA_FUEL_AGGREGATE_ASSN
            "BIT": "bituminous_coal",
            "SUB": "sub_bituminous_coal",
            "LIG": "lignite_coal",
            "COW": "all_coal",
            "NG": "natural_gas",
            "PC": "petroleum_coke",
            "PEL": "petroleum_liquids",
        },
        "sector_agg": {
            # match values in pudl.metadata.dfs.py:EIA_SECTOR_AGGREGATE_ASSN
            "1": "electric_utility",
            "2": "ipp_non_cogen",
            "3": "ipp_cogen",
            "4": "commercial_non_cogen",
            "5": "commercial_cogen",
            "6": "industrial_non_cogen",
            "7": "industrial_cogen",
            "94": "all_ipp",
            "96": "all_commercial",
            "97": "all_industrial",
            "98": "all_electric_power",  # all_IPP + regulated utilities
            "99": "all_sectors",
        },
        "temporal_agg": {
            "M": "monthly",
            "Q": "quarterly",
            "A": "annual",
        },
    }
    for col_name, mapping in mappings.items():
        keys.loc[:, col_name] = keys.loc[:, col_name].map(mapping)
        assert (
            keys.loc[:, col_name].notnull().all()
        ), f"{col_name} contains an unmapped category."
    keys = keys.astype("category")
    return keys