code: protected String stringWithoutHeader() {
  
          StringBuffer text = new StringBuffer();
  
          for (int i = 0; i < numInstances(); i++) {
              text.append(instance(i));
              if (i < numInstances() - 1) {
                  text.append('\n');
              }
          }
          return text.toString();
  
      }
docs: Returns the instances in the dataset as a string in ARFF format. Strings
  are quoted if they contain whitespace characters, or if they are a
  question mark.
  
  @return the dataset in ARFF format as a string