for(Iterator<UIComponent> children = getChildren().iterator(); children.hasNext();) {
UIComponent kid = children.next();
if(kid.isRendered() && kid instanceof Column) {
Column column = (Column) kid;
if(column.getValueExpression("filterBy") != null) {
filterMap.put(column.getClientId(FacesContext.getCurrentInstance()), column.getValueExpression("filterBy"));
}
}
}
}