docstr: Returns
  -------
  PriorFactory
docstr_tok: ["Returns","--","--","--","-","PriorFactory"]
code: def drop_unused_terms(self):
      """
      Returns
      -------
      PriorFactory
      """
      self.term_doc_mat = self.term_doc_mat.remove_terms(
          set(self.term_doc_mat.get_terms()) - set(self.priors.index)
      )
      self._reindex_priors()
      return self
  
imports: import pandas
  import numpy
  from scattertext.termranking import AbsoluteFrequencyRanker
  from scattertext.termsignificance.LogOddsRatioInformativeDirichletPiror import LogOddsRatioInformativeDirichletPrior
label_desc: Use image node_id 12 for calling the PriorFactory obj's underlying member method code with example usage: obj.drop_unused_terms() and returns: self