code: public String getGroupVariableName(DJGroup group) {
  		String columnToGroupByProperty = group.getColumnToGroupBy().getColumnProperty().getProperty();
  		return "variable-" + columnToGroupByProperty + "_" + getPercentageColumn().getColumnProperty().getProperty() + "_percentage";
  	}
docs: The group which the variable will be inside (mostly for reset)
  @param group (may be null)
  @return