/** Partitions the windowGroups into SortGroups based on compatible order by exprs. */
private List<SortGroup> collectSortGroups(List<WindowGroup> windowGroups) {
List<SortGroup> sortGroups = Lists.newArrayList();
for (WindowGroup windowGroup : windowGroups) {
boolean match = false;
for (SortGroup sortGroup : sortGroups) {
if (sortGroup.isCompatible(windowGroup)) {
sortGroup.add(windowGroup);
match = true;
break;
}
}
if (!match) sortGroups.add(new SortGroup(windowGroup));
}
return sortGroups;
}
