code: public PMMLPlanner setRetainOnlyActiveFields(){
  		Evaluator evaluator = getEvaluator();
  
  		Fields incomingFields = new Fields()
  			.append(FieldsUtil.getActiveFields(evaluator))
  			.append(FieldsUtil.getGroupFields(evaluator));
  
  		return setRetainedFields(incomingFields);
  	}
docs: Orders the retention of only those incoming fields that represent PMML function argument fields.
  
  @see #setRetainedFields(Fields)