Parameters
        ----------
        term_doc_matrix : TermDocMatrix
            Term document matrix object to compact
        Returns
        -------
        New term doc matrix

def compact(self, term_doc_matrix):
        '''
        Parameters
        ----------
        term_doc_matrix : TermDocMatrix
            Term document matrix object to compact
        Returns
        -------
        New term doc matrix
        '''
        rank_df = self.scorer.get_rank_df(term_doc_matrix)
        optimal_rank = self._find_optimal_rank(rank_df)
        compacted_term_doc_matrix = self._prune_higher_ranked_terms(term_doc_matrix, rank_df, optimal_rank)
        print('max terms', self.max_terms, 'optimal_rank', optimal_rank,
              'num_terms', compacted_term_doc_matrix.get_num_terms())
        return compacted_term_doc_matrix