Dart Lists Maps and Collections

Most apps handle groups of data — a list of products, a set of user tags, a dictionary of settings. Dart provides three main collection types: List, Map, and Set. Each serves a different purpose.

List — Ordered Collection

A List stores items in a specific order. Each item has an index starting at 0.

  Index:  [0]       [1]       [2]       [3]
          ┌─────┬─────────┬─────────┬──────────┐
  Items:  │Apple│  Mango  │ Banana  │ Grapes   │
          └─────┴─────────┴─────────┴──────────┘

List<String> fruits = ['Apple', 'Mango', 'Banana', 'Grapes'];

print(fruits[0]);      // Apple
print(fruits.length);  // 4

fruits.add('Orange');           // Add at end
fruits.insert(1, 'Kiwi');      // Add at index 1
fruits.remove('Mango');        // Remove by value
fruits.removeAt(0);            // Remove by index

print(fruits);  // [Kiwi, Banana, Grapes, Orange]

Common List Methods

Filtering and Transforming a List

List<int> scores = [45, 72, 88, 34, 91, 60];

// Keep only scores above 60
List<int> passed = scores.where((s) => s > 60).toList();
print(passed); // [72, 88, 91]

// Double every score
List<int> doubled = scores.map((s) => s * 2).toList();
print(doubled); // [90, 144, 176, 68, 182, 120]

Map — Key-Value Pairs

A Map stores data as key-value pairs, like a real-world dictionary where each word (key) has a definition (value).

  Key          Value
  ─────────    ───────────
  'name'   →   'Arjun'
  'age'    →   28
  'city'   →   'Delhi'

Map<String, dynamic> user = {
  'name': 'Arjun',
  'age': 28,
  'city': 'Delhi',
};

print(user['name']);   // Arjun
print(user['age']);    // 28

user['email'] = 'arjun@mail.com';  // Add new key
user['age'] = 29;                  // Update value
user.remove('city');               // Delete a key

print(user.keys);    // (name, age, email)
print(user.values);  // (Arjun, 29, arjun@mail.com)

Iterating Over a Map

user.forEach((key, value) {
  print('$key: $value');
});
// name: Arjun
// age: 29
// email: arjun@mail.com

Set — Unique Items Only

A Set is like a List but it never holds duplicates. Order is not guaranteed.

  List (allows duplicates):  [1, 2, 2, 3, 3, 3]
  Set  (unique only):        {1, 2, 3}

Set<String> tags = {'flutter', 'dart', 'mobile'};
tags.add('flutter');  // Duplicate — ignored silently
print(tags);          // {flutter, dart, mobile}

tags.add('web');
print(tags.contains('dart')); // true

Choosing the Right Collection

  Need ordered, indexed items?  → List
  Need key → value lookup?      → Map
  Need unique items only?       → Set

Spread Operator and Collection If

Dart supports powerful ways to build collections inline.

Spread Operator

List<int> a = [1, 2, 3];
List<int> b = [0, ...a, 4];  // Spreads a into b
print(b); // [0, 1, 2, 3, 4]

Collection If

bool isAdmin = true;

List<String> menu = [
  'Home',
  'Profile',
  if (isAdmin) 'Admin Panel',  // Included only if true
];

print(menu); // [Home, Profile, Admin Panel]

Lists Inside Flutter

Lists power most Flutter UIs. The ListView.builder widget takes a list and builds one row per item efficiently.

List<String> cities = ['Mumbai', 'Delhi', 'Bangalore'];

ListView.builder(
  itemCount: cities.length,
  itemBuilder: (context, index) {
    return ListTile(title: Text(cities[index]));
  },
)

  ┌─────────────────────────┐
  │ Mumbai                  │
  ├─────────────────────────┤
  │ Delhi                   │
  ├─────────────────────────┤
  │ Bangalore               │
  └─────────────────────────┘