groupSort<T, K> function

List<K> groupSort<T, K>(
  1. Iterable<T> iterable,
  2. K key(
    1. T
    ), [
  3. num valueComparator(
    1. List<T>,
    2. List<T>
    ) = ascending,
  4. num keyComparator(
    1. K,
    2. K
    ) = ascending,
])

Groups the specified iterable of elements according to the specified key function, sorts the groups according to the specified valueComparator for values and keyComparator for keys, and then returns a list of keys in sorted order.

If the comparison of values results in a tie (i.e., comparison returns 0), the keyComparator is used to break the tie and determine the order of the keys. If valueComparator is not provided, it defaults to ascending, and if keyComparator is not provided, it also defaults to ascending.

Implementation

List<K> groupSort<T, K>(Iterable<T> iterable, K Function(T) key,
    [num Function(List<T>, List<T>) valueComparator = ascending,
    num Function(K, K) keyComparator = ascending]) {
  return sort(group(iterable, key).entries, (g1, g2) {
    var comp = valueComparator(g1.value, g2.value);
    return comp != 0 ? comp : keyComparator(g1.key, g2.key);
  }).map((e) => e.key).toList();
}