Maps

Maps in Dart are collections of key-value pairs, where each key is associated with exactly one value. They are useful when we need to associate data with unique keys and can provide quick lookups by key. Here’s a guide to help us get started with Maps in Dart:

Creating a Map

We can create a map using the Map constructor or a map literal.

// Using Map constructor
Map<String, int> ages = Map<String, int>();

// Using map literal
Map<String, int> ages = {'Alice': 30, 'Bob': 25, 'Charlie': 35};

Adding and Updating Entries

We can add or update entries in a map by assigning a value to a key.

// Adding new entries
ages['David'] = 40;
ages['Eve'] = 22;

// Updating an existing entry
ages['Alice'] = 31; // Updates Alice's age to 31

Accessing Values

We can access the value associated with a key using the key.

int aliceAge = ages['Alice']; // 31
int bobAge = ages['Bob']; // 25

Removing Entries

We can remove entries from a map using the remove method.

ages.remove('Bob'); // Removes the entry with key 'Bob'

Iterating Over a Map

We can iterate over the entries in a map using a forEach loop, a for-in loop, or other iteration methods.

// Using forEach
ages.forEach((key, value) {
  print('$key: $value');
});

// Using for-in loop
for (var entry in ages.entries) {
  print('${entry.key}: ${entry.value}');
}

Checking for Keys or Values

We can check if a map contains a specific key or value using containsKey and containsValue.

bool hasAlice = ages.containsKey('Alice'); // true
bool hasAge30 = ages.containsValue(30); // false (because Alice's age was updated to 31)

Getting Keys and Values

We can get all keys or values in a map using the keys and values properties.

Iterable<String> keys = ages.keys; // ['Alice', 'Charlie', 'David', 'Eve']
Iterable<int> values = ages.values; // [31, 35, 40, 22]

Example

Here’s a small example demonstrating how to use maps in Dart:

void main() {
  Map<String, int> ages = {'Alice': 30, 'Bob': 25, 'Charlie': 35};

  // Adding new entries
  ages['David'] = 40;
  ages['Eve'] = 22;

  // Updating an existing entry
  ages['Alice'] = 31;

  // Accessing values
  print('Alice is ${ages['Alice']} years old.');

  // Removing an entry
  ages.remove('Bob');

  // Iterating over a map
  ages.forEach((key, value) {
    print('$key is $value years old.');
  });

  // Checking for keys or values
  print(ages.containsKey('Charlie')); // true
  print(ages.containsValue(30)); // false

  // Getting keys and values
  print('Keys: ${ages.keys}'); // Keys: (Alice, Charlie, David, Eve)
  print('Values: ${ages.values}'); // Values: (31, 35, 40, 22)
}

Maps in Dart provide powerful functionality for working with key-value pairs, making them ideal for many common programming tasks.

Dung (Donny) Nguyen

Senior Software Engineer