docstr: Core algorithm, which gathers the most common unigrams into a string.
docstr_tok: ["Core","algorithm",",","which","gathers","the","most","common","unigrams","into","a","string","."]
code: def get_prediction(self):
      """
      Core algorithm, which gathers the most common unigrams into a string.
      """
      # we always make the same prediction, so cache it for speed
      if self.unigram_cache is None:
          most_common = sorted(
              self.dict.freq.items(), key=lambda x: x[1], reverse=True
          )
          most_common = (
              (u, v) for u, v in most_common if self.is_valid_word(u)
          )
          most_common = islice(most_common, self.num_words)
          most_common = (u for u, v in most_common)
          self.unigram_cache = " ".join(list(most_common))
      return self.unigram_cache
  
imports: from typing import Optional
  from parlai.core.params import ParlaiParser
  from parlai.core.opt import Opt
  import json
  import re
  from parlai.core.agents import Agent
  from parlai.core.dict import DictionaryAgent
  from itertools import islice
  from parlai.utils.io import PathManager
label_desc: Use image node_id 7 for calling the UnigramAgent obj's underlying member method code with example usage: obj.get_prediction() and returns: self