Scala Collections

Senthil Nayagan
Written by Senthil Nayagan on  - 2 Mins Read

In programming, a collection is an object that groups multiple elements into a single unit. A collection is like a container that can store a variety of items.
Scala Collections

Introduction to collections

A collection is an object in programming that groups multiple elements into a single unit. A collection is comparable to a container that can hold various items. A collection has an underlying data structure that is used to store, manipulate, and retrieve aggregate data in an efficient manner. When collections are used, readability and maintenance of code are enhanced.

Collections in Scala

Scala has a very rich collections library, located under the scala.collection package. There are two types of collections in Scala:

  • Mutable collections
  • Immutable collections

Scala collections vs Java collections: Scala collections are notably distinct from Java collections. For example, the Scala List class differs significantly from the Java List classes, including the immutable nature of the Scala List.

Mutable collections

A mutable collection can be modified or extended in place. This means that we can modify, add, or remove elements from a collection with side effects. All mutable collection classes are present in the scala.collection.mutable package.

Immutable collections

In contrast, immutable collections never change. There are still operations that simulate additions, deletions, and updates, but each of these operations returns a new collection and leaves the original collection unchanged. All immutable collections are present under scala.collection.immutable.

The collections in scala.collection are supertypes of scala.collection.mutable and scala.collection.immutable. The base operations are added to the types in the scala.collection package, while the immutable and mutable operations are added to the types in the other two packages.

A high-level view of the Scala collections


Collections table

Frequently asked questions (FAQ)

What is InPlace transformation operation?

Instead of always returning a new collection after a map or filter operation, mutable collections have a couple of new operations (filterInPlace and mapInPlace) that let us change the elements right where they are (in-place). These new operations change the source collection.

val buf1 = ArrayBuffer(0, 1, 2, 3, 5, 6, 8, 9)
buf1.filterInPlace(_ % 2 == 0) 
buf1 // ArrayBuffer(0, 2, 6, 8)

val buf2 = ArrayBuffer(0, 1, 2, 3, 5, 6, 8, 9)
buf2.mapInPlace(_ * 2)
buf2 // ArrayBuffer(0, 2, 4, 6, 10, 12, 16, 18)

What are trasnformer methods?

Transformer methods are collection methods that transform an input collection into a new output collection based on an algorithm we provide.

The transformer methods are as follows:

  • map
  • filter
  • reverse


comments powered by Disqus