addF.setAttributeIndex(0);
addF.setAttributeIndex("first");
  public void addInstanceNumberAttribute() {    String originalRelationName = m_plotInstances.relationName();    try {      Add addF = new Add();      addF.setAttributeName("Instance_number");      addF.setAttributeIndex(0);      addF.setInputFormat(m_plotInstances);      m_plotInstances = Filter.useFilter(m_plotInstances, addF);      m_plotInstances.setClassIndex(m_plotInstances.numAttributes()-1);      for (int i = 0; i < m_plotInstances.numInstances(); i++) {	m_plotInstances.instance(i).setValue(0,(double)i);      }      m_plotInstances.setRelationName(originalRelationName);    } catch (Exception ex) {      ex.printStackTrace();    }  }