code: def columns_dataset(self):
          
          data = {}
          words_total = {}
  
          for instance, words in self.raw_dataset.items():
              words_item_total = {}
              for word in words:
                  words_total.setdefault(word, 0)
                  words_item_total.setdefault(word, 0)
                  words_total[word] += 1
                  words_item_total[word] += 1
              data[instance] = words_item_total
  
          columns = sorted(words_total.keys(),
                           key=lambda w: words_total[w],
                           reverse=True)[:250]
          columns = sorted(columns)
          dataset = {}
          for instance in data.keys():
              dataset[instance] = [data[instance].get(word, 0)
                                   for word in columns]
          return columns, dataset
docs: Generate the columns and the whole dataset.