How to sort list of maps where each map is a pair of key and another list of objects

I have the following list in Dart, which is a List of Map which maps a key to a list of MyClass objects:

class MyClass {
  final String name;
  final int age;

  MyClass({
    required this.name,
    required this.age,
  });
}

void main() { 
  MyClass obj1 = MyClass(name: "aa", age: 10);
  MyClass obj2 = MyClass(name: "bb", age: 20);
  MyClass obj3 = MyClass(name: "cc", age: 30);
  MyClass obj4 = MyClass(name: "dd", age: 40);
  MyClass obj5 = MyClass(name: "ee", age: 50);
  MyClass obj6 = MyClass(name: "ff", age: 60);
  
   List<Map<String, List<Object>>> myList = [
  { '3' : [obj1, obj2]},
  { '1' : [obj3, obj4]},
  { '2' : [obj5, obj6]},
];

  print(myList);
}

I need to sort this list based on keys in descending order so that keys need to be in the order ‘3’, ‘2’, ‘1’ in the main list.

How can I do this?

>Solution :

You can give sort() on List a compare method which define how elements should be sorted. So in your case, we can do something like this:

void main() {
  List<Map<String, List<MyClass>>> myList = [
    { '3' : [MyClass(name: 'ifredom',age:23), MyClass(name: 'aaa',age:13)]},
    { '1' : [MyClass(name: 'JackMa',age:61), MyClass(name: 'bbb',age:33)]},
    { '2' : [MyClass(name: 'zhazhahui',age:48), MyClass(name: 'ccc',age:29)]}
  ];

  myList.forEach(print);
  // {3: [MyClass(name: ifredom, age: 23), MyClass(name: aaa, age: 13)]}
  // {1: [MyClass(name: JackMa, age: 61), MyClass(name: bbb, age: 33)]}
  // {2: [MyClass(name: zhazhahui, age: 48), MyClass(name: ccc, age: 29)]}

  myList.sort((a, b) => b.keys.first.compareTo(a.keys.first));

  myList.forEach(print);
  // {3: [MyClass(name: ifredom, age: 23), MyClass(name: aaa, age: 13)]}
  // {2: [MyClass(name: zhazhahui, age: 48), MyClass(name: ccc, age: 29)]}
  // {1: [MyClass(name: JackMa, age: 61), MyClass(name: bbb, age: 33)]}
}

class MyClass {
  final String name;
  final int age;

  MyClass({required this.name, required this.age,});

  @override
  String toString() => 'MyClass(name: $name, age: $age)';
}

Notice that we do assume here that each Map in your first List only contains one key and then sort based on this.