def remove_terms_used_in_less_than_num_docs(self, threshold):
        '''
        Parameters
        ----------
        threshold: int
            Minimum number of documents term should appear in to be kept

        Returns
        -------
        TermDocMatrix, new object with terms removed.
        '''
        term_counts = self._X.astype(bool).astype(int).sum(axis=0).A[0]
        terms_to_remove = np.where(term_counts < threshold)[0]
        return self.remove_terms_by_indices(terms_to_remove)