default String getOrderedColumnKeys() {
        return getColumns()
                .stream()
                .map(e -> e.getColumnKey())
                .collect(Collectors.joining(","));
    }
Return each {@link Row} in a Column Group.
@param context  the {@link FacesContext}
@param cg the {@link ColumnGroup} to get
@param skipUnrendered If unrendered components should be skipped
@param callback The callback, which will be invoked for each row. If it returns false, the algorithm will be cancelled
@return false when the algorithm was cancelled
primefaces/src/main/java/org/primefaces/component/api/ColumnAware.java