Collections in Scala

In this lesson, you will learn about collections in Scala. Collections are used to store, organize, and process groups of data efficiently.

Scala provides a rich and powerful collection library that supports both immutable and mutable data structures.

What Is a Collection?

A collection is a container that holds multiple values. These values can be processed together using built-in operations.

Instead of working with single variables, collections allow you to work with groups of data in a clean and expressive way.

Why Collections Are Important

Collections allow you to:

• Store multiple values efficiently
• Perform operations like filtering and mapping
• Write concise and readable code
• Process large datasets easily

Immutable vs Mutable Collections

Scala collections are divided into two main categories:

• Immutable collections – cannot be changed after creation
• Mutable collections – can be modified

By default, Scala encourages the use of immutable collections for safer and more predictable code.

Common Collection Types

Scala provides several commonly used collection types:

• List
• Array
• Set
• Map

In this lesson, you will get an overview of these collections. Each one will be explained in detail in upcoming lessons.

Creating a List

A List is an immutable collection that stores ordered elements.

val numbers = List(1, 2, 3, 4, 5)
println(numbers)

Once created, the list cannot be modified.

Accessing List Elements

You can access elements using index-based access.

println(numbers(0))
println(numbers(2))

Scala uses zero-based indexing.

Creating an Array

An Array is a mutable collection. Its elements can be modified after creation.

val fruits = Array("Apple", "Banana", "Orange")
fruits(1) = "Mango"
println(fruits.toList)

Arrays are useful when you need mutable, index-based data.

Creating a Set

A Set stores unique elements only. Duplicate values are automatically removed.

val uniqueNumbers = Set(1, 2, 2, 3, 4)
println(uniqueNumbers)

Sets are useful when uniqueness matters.

Creating a Map

A Map stores data as key-value pairs.

val studentAges = Map(
  "Alice" -> 22,
  "Bob" -> 24
)

println(studentAges("Alice"))

Maps are useful for fast lookups based on keys.

Basic Collection Operations

Scala collections support many built-in operations.

Looping Through a Collection

for (n <- numbers) {
  println(n)
}

Using map()

The map() method transforms each element.

val doubled = numbers.map(n => n * 2)
println(doubled)

Using filter()

The filter() method selects elements based on a condition.

val evenNumbers = numbers.filter(n => n % 2 == 0)
println(evenNumbers)

Why Scala Collections Are Powerful

Scala collections are:

• Type-safe
• Immutable by default
• Rich in built-in operations
• Optimized for functional programming

📝 Practice Exercises

Exercise 1

Create a list of five numbers and print it.

Exercise 2

Create a set with duplicate values and observe the output.

Exercise 3

Create a map that stores country names and capitals.

✅ Practice Answers

Answer 1

val nums = List(10, 20, 30, 40, 50)
println(nums)

Answer 2

val data = Set(1, 1, 2, 3, 3)
println(data)

Answer 3

val capitals = Map(
  "India" -> "New Delhi",
  "USA" -> "Washington"
)
println(capitals)

What’s Next?

In the next lesson, you will explore Arrays and Lists in detail, including performance differences and real-world use cases.