groupBy<K> method

Map<K, Iterable<T>> groupBy<K>(K key(T element))

Groups the elements of the iterable by a specified key function. The result is a map where each key corresponds to a list of elements that share the same key.

Example usage:

class Person {
  final String name;
  final String role;
  const Person(this.name, this.role);
}

void main() {
  List<Person> people = const [
    Person('John', 'Manager'),
    Person('Alice', 'Engineer'),
    Person('Bob', 'Engineer'),
    Person('Charlie', 'Manager'),
    Person('Eve', 'Designer'),
  ];

  Map<String, Iterable<Person>> groupedPeople = people.groupBy((person) => person.role);

  groupedPeople.forEach((role, people) {
    print('$role: ${people.map((person) => person.name).join(', ')}');
  });
}

Implementation

Map<K, Iterable<T>> groupBy<K>(K Function(T element) key) {
  final map = <K, List<T>>{};
  for (final element in this) {
    final keyValue = key(element);
    if (!map.containsKey(keyValue)) {
      map[keyValue] = [];
    }
    map[keyValue]?.add(element);
  }
  return map;
}