如何在dart中按多个值对列表进行分组

extension GroupByExtension<T> on Iterable<T> {
  Map<String, List<T>> groupBy(List<String> properties) {
    Map<String, List<T>> result = {};

    for (var element in this) {
      String key = '';
      for (var property in properties) {
        key += element[property].toString();
      }

      if (!result.containsKey(key)) {
        result[key] = [];
      }
      result[key]!.add(element);
    }

    return result;
  }
}

void main() {
  List<Map<String, dynamic>> data = [
    {'name': 'Alice', 'age': 25, 'city': 'New York'},
    {'name': 'Bob', 'age': 30, 'city': 'London'},
    {'name': 'Charlie', 'age': 25, 'city': 'New York'},
    {'name': 'Dave', 'age': 30, 'city': 'London'},
  ];

  List<String> properties = ['age', 'city'];
  Map<String, List<Map<String, dynamic>>> groupedData = data.groupBy(properties);

  for (var entry in groupedData.entries) {
    print('Group ${entry.key}:');
    for (var element in entry.value) {
      print(element);
    }
    print('');
  }
}