Flutter & Dart: Sorting a List of Objects/Maps by Date

This practical, code-centric article will show you how to sort a list of objects/maps by date in Flutter. The point is to use the sort() method of the List class and pass a custom comparison function that uses the compareTo() method of the DateTime class:

myList.sort ((a, b) {
  // for ascending order
  return a.date.compareTo (b.date); 
   
  // for descending order
  // return b.date.compareTo (a.date); 
});

For more clarity, see the following complete examples.

Sorting a List of Objects by Date

Let’s say you have a list of users. The information of each user is stored in an object, and your boss asks you to reorder these users by their join date. The example below will show you to solve this:

// this class is used to create User objects
class User {
  final String name;
  final String email;
  final DateTime joinDate;

  User({required this.name, required this.email, required this.joinDate});

  @override
  String toString() {
    return 'User{name: $name, email: $email, joinDate: $joinDate}';
  }
}

void main() {
  // list of users
  List<User> users = [
    User(
        name: 'Jack',
        email: '[email protected]',
        joinDate: DateTime(2022, 6, 1)),
    User(
        name: 'John',
        email: '[email protected]',
        joinDate: DateTime(2020, 1, 1)),
    User(
        name: 'Jane',
        email: '[email protected]',
        joinDate: DateTime(2021, 5, 12)),
    User(
        name: 'Jill',
        email: '[email protected]',
        joinDate: DateTime(2023, 7, 1))
  ];

  // sort by joinDate: ascending
  final sortedUsersAsc = users.map((user) => user).toList()
    ..sort((a, b) => a.joinDate.compareTo(b.joinDate));

  // sort by joinDate: descending
  final sortedUsersDesc = users.map((user) => user).toList()
    ..sort((a, b) => b.joinDate.compareTo(a.joinDate));

  print('Sorted by joinDate: ascending');
  sortedUsersAsc.forEach((user) => print(user.toString()));

  print('Sorted by joinDate: descending');
  sortedUsersDesc.forEach((user) => print(user.toString()));
}

Output:

Sorted by joinDate: ascending
User{name: John, email: [email protected], joinDate: 2020-01-01 00:00:00.000}
User{name: Jane, email: [email protected], joinDate: 2021-05-12 00:00:00.000}
User{name: Jack, email: [email protected], joinDate: 2022-06-01 00:00:00.000}
User{name: Jill, email: [email protected], joinDate: 2023-07-01 00:00:00.000}
Sorted by joinDate: descending
User{name: Jill, email: [email protected], joinDate: 2023-07-01 00:00:00.000}
User{name: Jack, email: [email protected], joinDate: 2022-06-01 00:00:00.000}
User{name: Jane, email: [email protected], joinDate: 2021-05-12 00:00:00.000}
User{name: John, email: [email protected], joinDate: 2020-01-01 00:00:00.000}

Sorting a List of Maps by Date

In this example, the information about a user is stored in a map instead of an object. Besides that, the join date of a user is a string, not a DateTime object. Therefore, we will need to parse it into a DateTime object first using the DateTime.parse() or DateTime.tryParse() method before performing the comparison.

The code:

void main() {
  final List<Map<String, dynamic>> users = [
    {
      "name": "Jack",
      "email": "[email protected]",
      "joinDate": "2023-06-01",
    },
    {
      "name": "John",
      "email": "[email protected]",
      "joinDate": "2020-01-01",
    },
    {
      "name": "Jane",
      "email": "[email protected]",
      "joinDate": "2021-05-12",
    },
    {
      "name": "Jill",
      "email": "[email protected]",
      "joinDate": "2023-07-01",
    }
  ];

  // sort users by joinDate: ascending
  final sortedUsersAsc = users.map((user) => user).toList()
    ..sort((a, b) =>
        DateTime.parse(a["joinDate"]).compareTo(DateTime.parse(b["joinDate"])));

  // sort users by joinDate: descending
  final sortedUsersDesc = users.map((user) => user).toList()
    ..sort((a, b) =>
        DateTime.parse(b["joinDate"]).compareTo(DateTime.parse(a["joinDate"])));

  print("Sorted users by ascending joinDate:");
  print(sortedUsersAsc);

  print("Sorted users by descending joinDate:");
  print(sortedUsersDesc);
}

Output:

Sorted users by ascending joinDate:
[
  {name: John, email: [email protected], joinDate: 2020-01-01}, 
  {name: Jane, email: [email protected], joinDate: 2021-05-12}, 
  {name: Jack, email: [email protected], joinDate: 2023-06-01}, 
  {name: Jill, email: [email protected], joinDate: 2023-07-01}
]

Sorted users by descending joinDate:
[ 
  {name: Jill, email: [email protected], joinDate: 2023-07-01}, 
  {name: Jack, email: [email protected], joinDate: 2023-06-01}, 
  {name: Jane, email: [email protected], joinDate: 2021-05-12}, 
  {name: John, email: [email protected], joinDate: 2020-01-01}
]

That’s it. Further reading:

• Working with ReorderableListView in Flutter
• Flutter: Adding a Border to an Icon Button (2 Approaches)
• Flutter StreamBuilder: Tutorial & Examples (Updated)
• Working with Timer and Timer.periodic in Flutter
• Using GetX to make GET/POST requests in Flutter
• Flutter & Dart: Get a list of dates between 2 given dates

You can also tour around our Flutter topic page or Dart topic page for the most recent tutorials and examples.