Group and sort map in a predefined order - flutter

Question

Here is an extension to group my tasks
/// EXTENSION
Map<K, List<T>> groupBy<T, K>(K key(T e)) {
Map<K, List<T>> map = {};
for (final element in this) {
var list = map.putIfAbsent(key(element as T), () => []);
list.add(element);
}
return map;
}
/// CODE
final List<String> requiredPrioritySortOrder = ['df','sc','de','dd'];
final Map<String, List<Task>> tasksByPriority = _selectedTasks.groupBy<Task, String>((e) => e.priority);
As a result, I have received a map but the sort order change every time after the task update.
How to sort tasksByPriority Map by key in a predefined order (requiredPrioritySortOrder).
Thanks :)

Answer 1

I am already find a solution but maybe there is another way?
_selectedTasks.groupBy<Task, String>((e) => e.priority, order:['sc','df']);
Map<K, List<T>> groupBy<T, K>(K key(T e), {Iterable order = const []}) {
Map<K, List<T>> mapped = {};
Map<K, List<T>> sorted = {};
for (final e in this) {
List list = mapped.putIfAbsent(key(e as T), () => []);
list.add(e);
}
if (order.isNotEmpty) {
order.forEach((e) {
if (mapped[e] != null) {
sorted[e] = mapped[e]!;
}
});
return sorted;
}
return mapped;
}