Swift Collections

📦 Swift Collections – Complete Beginner to Interview Guide

In Swift, collections are used to store multiple values in a single variable.
Swift provides three main collection types:

1️⃣ Array
2️⃣ Dictionary
3️⃣ Set

These are core concepts for Swift programming, exams, and interviews.

1️⃣ Array in Swift ⭐

An Array stores an ordered list of values of the same type.

Declaration

Access Elements

Output

Add Elements

Output

Loop Through Array

2️⃣ Dictionary in Swift ⭐⭐

A Dictionary stores data in key–value pairs.

Declaration

Access Value

Output

📌 Use ! when you are sure the key exists.

Add / Update Value

Loop Through Dictionary

3️⃣ Set in Swift ⭐⭐

A Set stores unique, unordered values.

Declaration

Output

📌 Duplicate values are automatically removed.

Add & Remove

4️⃣ Mutable vs Immutable Collections ⭐⭐

Mutable (can change)

Immutable (cannot change)

5️⃣ Common Collection Operations ⭐⭐

Count

Check Empty

Contains

6️⃣ Collection Functions (Very Important) ⭐⭐⭐

map

Output-1:

filter

Output-2 :

reduce

Output-3:

7️⃣ Array vs Set vs Dictionary ⭐⭐⭐

8️⃣ When to Use What ❓

✔ Array → ordered data, indexing
✔ Set → unique values, fast lookup
✔ Dictionary → key–value mapping

9️⃣ Common Mistakes ❌

❌ Using wrong collection type
❌ Force-unwrapping dictionary values unsafely
❌ Expecting order in Set
❌ Modifying let collections

📌 Interview Questions (Swift Collections)

Q1. Difference between Array and Set?
👉 Array allows duplicates, Set does not

Q2. Is Dictionary ordered?
👉 No

Q3. Which collection is fastest for search?
👉 Set

Q4. What does map() do?
👉 Transforms elements

✅ Summary

✔ Swift has Array, Dictionary, Set
✔ Arrays are ordered
✔ Sets store unique values
✔ Dictionaries use key–value pairs
✔ map, filter, reduce are must-know
✔ Very important for Swift interviews