def symbols_to_data(vocab, list_of_symbols):
  """ Transform the symbol to original word.
  Args:
    vocab: a list of words, the dictionary.
    list_of_symbols: a list of string lists. """
  list_of_sentences = []
  for symbols in list_of_symbols: # a list of symbols
    sentence = [vocab[i] for i in symbols]
    list_of_sentences.append(sentence)
  return list_of_sentences