Convert categorical columns to numeric values.

        Parameters
        ----------
        X : pandas.DataFrame
            Data to encode.

        Returns
        -------
        Xt : pandas.DataFrame
            Encoded data.

def transform(self, X):
        """Convert categorical columns to numeric values.

        Parameters
        ----------
        X : pandas.DataFrame
            Data to encode.

        Returns
        -------
        Xt : pandas.DataFrame
            Encoded data.
        """
        check_is_fitted(self, "encoded_columns_")
        check_columns_exist(X.columns, self.feature_names_)

        Xt = X.copy()
        for col, cat in self.categories_.items():
            Xt[col].cat.set_categories(cat, inplace=True)

        new_data = self._encode(Xt, self.feature_names_)
        return new_data.loc[:, self.encoded_columns_]