Create list from multiple lists with a property is equal

My row lists:

List rowlist = [Student(name: 'John',age: 12),
             Student(name: 'Kity',age: 13),
             Student(name: 'Micle',age: 14),
             Student(name: 'Jack',age: 12),
             Student(name: 'Cha',age: 13),
             Student(name: 'Duc',age: 13),
             Student(name: 'Ran',age: 12)]

Expected result:

List result = [
               [
                Student(name: 'John',age: 12),
                Student(name: 'Jack',age: 12),
                Student(name: 'Ran',age: 12),
               ],
               [
                Student(name: 'Kity',age: 13),
                Student(name: 'Cha',age: 13),
                Student(name: 'Duc',age: 13),
               ],
               [
                Student(name: 'Micle',age: 14),
               ]
             ]

I need to create a new list of list wherein each list is added by Student with age field is equal. What is the best way for the result?.

>Solution :

If you use the collection package. You can use the groupListsBy method to group all of the students by age.

Map<int, List<Student>> result = rowlist.groupListsBy((student) => student.age);

The above however, returns the data as a Map<int, List<Student>. You can convert this to a List<List<Student>> by calling .values.toList().

List<List<Student>> result = rowlist.groupListsBy((student) => student.age).values.toList();

Complete example:

import 'package:collection/collection.dart';

void main() {
  List<Student> rowlist = [
    Student(name: 'John', age: 12),
    Student(name: 'Kity', age: 13),
    Student(name: 'Micle', age: 14),
    Student(name: 'Jack', age: 12),
    Student(name: 'Cha', age: 13),
    Student(name: 'Duc', age: 13),
    Student(name: 'Ran', age: 12),
  ];

  List<List<Student>> result =
      rowlist.groupListsBy((student) => student.age).values.toList();

  print(result);
}

class Student {
  final String name;
  final int age;
  const Student({required this.name, required this.age});
  @override
  String toString() => 'Student(name: $name, age: $age)';
}