Get the boolean mask indicating which features are selected
        Returns
        -------
        support : boolean array of shape [# input features]
            An element is True iff its corresponding feature is selected for
            retention.

def _get_support_mask(self):
        """
        Get the boolean mask indicating which features are selected
        Returns
        -------
        support : boolean array of shape [# input features]
            An element is True iff its corresponding feature is selected for
            retention.
        """
        check_is_fitted(self, 'feat_list_idx')
        n_features = len(self.feature_names)
        mask = np.zeros(n_features, dtype=bool)
        mask[np.asarray(self.feat_list_idx)] = True

        return mask