groupBy<T> method

Map<T, List<S>> groupBy<T>(T key(S))

Implementation

Map<T, List<S>> groupBy<T>(T Function(S) key) {
  final map = <T, List<S>>{};
  for (final element in this) {
    (map[key(element)] ??= []).add(element);
  }
  return map;
}