def _values_for_factorize(self) -> Tuple[np.ndarray, Any]:
return self.astype(object), np.nan<EOL>
Return an array and missing value suitable for factorization.

Returns
-------
values : ndarray

    An array suitable for factorization. This should maintain order
    and be a supported dtype (Float64, Int64, UInt64, String, Object).
    By default, the extension array is cast to object dtype.
na_value : object
    The value in `values` to consider missing. This will be treated
    as NA in the factorization routines, so it will be coded as
    `na_sentinal` and not included in `uniques`. By default,
    ``np.nan`` is used.

Notes
-----
The values returned by this method are also used in
:func:`pandas.util.hash_pandas_object`.