code: def discard(self, min_freq, unknown_token):
          
          freq = 0
          ret = Counter({})
          for token, count in self.items():
              if count < min_freq:
                  freq += count
              else:
                  ret[token] = count
          ret[unknown_token] = ret.get(unknown_token, 0) + freq
          return ret
docs: Discards tokens with frequency below min_frequency and represents them
          as `unknown_token`.
  
          Parameters
          ----------
          min_freq: int
              Tokens whose frequency is under min_freq is counted as `unknown_token` in
              the Counter returned.
          unknown_token: str
              The representation for any unknown token.
  
          Returns
          -------
          The Counter instance.
  
          Examples
          --------
          >>> a = gluonnlp.data.Counter({'a': 10, 'b': 1, 'c': 1})
          >>> a.discard(3, '<unk>')
          Counter({'a': 10, '<unk>': 2})