Map in dart example

main.dart

void main() {
  // Creating a map of key-value pairs (int to String)
  Map<int, String> studentData = {
    3620301111: 'Ololade',
    3620302222: 'Chukwuemeka',
    3620303333: 'Umar',
  };

  // Accessing values using keys
  String ololadeName = studentData[3620301111]!; // 'Ololade'

  // Adding a new key-value pair
  studentData[3620304444] = 'Olumide';

  // Checking if a key exists in the map
  bool isChukwuemekaPresent = studentData.containsKey(3620302222); // true

  // Removing a key-value pair
  studentData.remove(3620303333);

  // Finding the number of key-value pairs
  int numberOfPeople = studentData.length; // 3

  // Iterating through the map
  studentData.forEach((matric, name) {
    print('$matric belongs to $name');
  });

  // Maps can have keys and values of different types
  Map<int, dynamic> person = {
    3620305555: 'Chinonso',
    3620306666: 29,
    3620307777: false,
  };

  // Creating an empty map and adding key-value pairs later
  Map<int, double> emptyMap = {};
  emptyMap[3620308888] = 175.5;

  // ================== MAP PROPERTIES

  // 1. length → int (Returns the number of key-value pairs)
  int mapLength = studentData.length;

  // 2. isEmpty → bool (Returns true if the map is empty)
  bool isMapEmpty = studentData.isEmpty;

  // 3. isNotEmpty → bool (Returns true if the map is not empty)
  bool isMapNotEmpty = studentData.isNotEmpty;

  // 4. keys → Iterable<K> (Returns an iterable of the map's keys)
  Iterable<int> personKeys = person.keys;

  // 5. values → Iterable<V> (Returns an iterable of the map's values)
  Iterable<dynamic> personValues = person.values;

  // ================== MAP METHODS

  // 1. putIfAbsent(key, ifAbsent) → V (Puts a key-value pair in the map if the key does not exist)
  studentData.putIfAbsent(3620309999, () => 'Ngozi');

  // 2. update(key, update, {ifAbsent}) → V (Updates the value for the given key or adds a new key-value pair if the key does not exist)
  studentData.update(3620302222, (value) => 'Chukwuemeka', ifAbsent: () => 'Chukwuemeka');

  // 3. clear() → void (Removes all key-value pairs from the map)
  studentData.clear();

  // 4. removeWhere(predicate) → void (Removes key-value pairs that satisfy a condition)
  person.removeWhere((key, value) => value is bool && !value);

  // 5. containsValue(value) → bool (Checks if the map contains a specific value)
  bool hasValue = studentData.containsValue('Chinwe');

  // 6. map() → Map<K2, V2> (Creates a new map by applying a function to each key-value pair)
  Map<int, String> namesToGreetings = person.map((key, value) {
    if (key == 3620305555) {
      return MapEntry(key, 'Hello, $value');
    }
    return MapEntry(key, value.toString());
  });

  // 7. clear() → void (Removes all key-value pairs from the map)
  studentData.clear();
}