docs: def to_arff(self):
          '''
          Returns the "wordified" representation in ARFF.
  
              :rtype: str
          '''
          arff_string = "@RELATION " + self.target_table.name + "\n\n"
          words = set()
          for document in self.resulting_documents:
              for word in document:
                  words.add(word)
          words = sorted(words)
  
          for i, word in enumerate(words):
              arff_string += "@ATTRIBUTE '" + word.replace("'", "") + "' REAL\n"
  
          arff_string += "@ATTRIBUTE class {" + ','.join(set([str(a) for a in self.resulting_classes])) + "}\n\n@DATA\n"
  
          self.word_features = []
          for doc_idx in range(len(self.resulting_documents)):
              features = []
              for word in words:
                  if word not in self.word_features:
                      self.word_features.append(word)
                  if word in self.tf_idfs[doc_idx]:
                      features.append(str(self.tf_idfs[doc_idx][word]))
                  else:
                      features.append("0")
              features.append(str(self.resulting_classes[doc_idx]))
  
              arff_string += ','.join(features)
              arff_string += "\n"
  
          return arff_string