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Introduction to Scala Collections

What are Collections?

Collections in Scala are data structures that allow you to store and manipulate groups of data. They provide various methods to perform operations on data such as adding, removing, and transforming elements. Scala collections are divided into two main categories: mutable and immutable collections.

Immutable Collections

Immutable collections cannot be modified after they are created. Any operation that appears to modify an immutable collection will instead return a new collection. This feature is particularly useful in functional programming as it helps in avoiding side effects.

Examples of Immutable Collections:

List

A List is a linear collection that maintains the order of elements.

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

Set

A Set is a collection of unique elements.

val uniqueNumbers = Set(1, 2, 3, 4, 5)

Map

A Map is a collection of key-value pairs.

val ages = Map("Alice" -> 25, "Bob" -> 30)

Mutable Collections

Mutable collections can be changed after they are created. You can add, remove, or update elements without creating a new collection. This flexibility comes at the cost of potential side effects, so care must be taken when using them in concurrent or functional programming scenarios.

Examples of Mutable Collections:

Mutable List

A mutable list allows for modification of its elements.

import scala.collection.mutable.ListBuffer
val mutableList = ListBuffer(1, 2, 3)
mutableList += 4

Mutable Set

A mutable set allows for dynamic addition and removal of elements.

import scala.collection.mutable.Set
val mutableSet = Set(1, 2, 3)
mutableSet.add(4)

Mutable Map

A mutable map allows for dynamic changes to key-value pairs.

import scala.collection.mutable.Map
val mutableMap = Map("Alice" -> 25)
mutableMap("Bob") = 30

Common Operations on Collections

Scala collections come with a rich set of operations that allow you to manipulate data easily. Here are some common operations:

  • Map: Transform each element of the collection.
  • Filter: Select elements based on a predicate.
  • Reduce: Combine elements into a single value.
  • Fold: Similar to reduce but allows an initial value.

Example of Common Operations:

val numbers = List(1, 2, 3, 4, 5)
val squares = numbers.map(x => x * x)
val evenNumbers = numbers.filter(x => x % 2 == 0)
Output: squares: List(1, 4, 9, 16, 25), evenNumbers: List(2, 4)

Conclusion

Scala collections are powerful and flexible tools that can help you manage data efficiently. Understanding the differences between mutable and immutable collections, along with their common operations, will greatly enhance your programming skills in Scala. As you continue to learn Scala, you will find collections to be an integral part of your coding experience.