flip method

Map<V, List<K>> flip()

Implementation

Map<V, List<K>> flip() {
  Map<V, List<K>> map = {};
  for (K key in keys) {
    V value = this[key]!;
    if (map.containsKey(value)) {
      map[value]!.add(key);
    } else {
      map[value] = [key];
    }
  }
  return map;
}