unique method

Map<K, V> unique()

Implementation

Map<K, V> unique() {
  Map<K, V> result = {};
  for (final value in {...values}) {
    final firstKey = keys.firstWhere((key) => this[key] == value);
    if (firstKey != null) {
      result[firstKey] = value;
    }
  }
  return result;
}