What is the difference between set vs map and where to use which one provide me with some-example ?

Overview

Set

Map

Set — Unique, Unordered Collection

A

Set

dartCopy
// Creating a Set
final fruits = {'apple', 'banana', 'orange'};
final numbers = <int>{1, 2, 3, 4, 5};
final empty = <String>{};

// Adding elements
fruits.add('grape');      // Adds
fruits.add('apple');      // ❌ Duplicate — ignored silently
print(fruits); // {apple, banana, orange, grape}

// Checking membership — O(1)
print(fruits.contains('apple')); // true
print(fruits.contains('mango')); // false

// Set operations
final a = {1, 2, 3, 4};
final b = {3, 4, 5, 6};
print(a.union(b));        // {1, 2, 3, 4, 5, 6}
print(a.intersection(b)); // {3, 4}
print(a.difference(b));   // {1, 2}

Map — Key-Value Pairs

A

Map

dartCopy
// Creating a Map
final person = {'name': 'Alice', 'age': '28', 'city': 'Mumbai'};
final scores = <String, int>{'Math': 95, 'Science': 88};

// Access by key — O(1)
print(person['name']);  // Alice
print(scores['Math']);  // 95

// Add / Update
scores['English'] = 92; // Add new key
scores['Math'] = 98;    // Update existing

// Check key/value existence
print(scores.containsKey('Math'));   // true
print(scores.containsValue(88));    // true

// Iterate
scores.forEach((key, value) => print('$key: $value'));

// Null safety
print(scores['Art'] ?? 0); // 0 (key doesn't exist)

Key Differences

{1, 2, 3}

{'key': 'value'}

<int>{}

{}

<String,int>{}

⚠️

textCopy

{}

creates an empty Map, not an empty Set! Use

textCopy

<T>{}

for empty Sets.

When to Use Which

Set

Set

Set

Map

Map

Map<String, int>

Map

Practical Examples

dartCopy
// Set — remove duplicates from list
final list = [1, 2, 2, 3, 3, 4];
final unique = list.toSet().toList(); // [1, 2, 3, 4]

// Map — word count
final words = ['apple', 'banana', 'apple', 'cherry'];
final count = <String, int>{};
for (final w in words) {
  count[w] = (count[w] ?? 0) + 1;
}
print(count); // {apple: 2, banana: 1, cherry: 1}

Quick Rule: Need unique items? → Set. Need key-value lookup? → Map.