Scala Tutorial - Learn How To Use Scala's Immutable List

By Nadim Bahadoor | Last updated: July 25, 2017 at 14:32 pm

Overview

In this tutorial, we will learn how to use Scala's Immutable List and perform common operations such as initialization, appending or prepending elements and accessing elements within the List.

 

More advanced functions such as aggregate, fold, reduce, map, flatMap etc on the Immutable List will be discussed in Chapter 8 on Collection Functions.

Steps

1. How to initialize an immutable List with 3 elements

The code below shows how to initialize an immutable List with 3 elements.


println("Step 1: How to initialize an immutable List with 3 elements")
val list1: List[String] = List("Plain Donut","Strawberry Donut","Chocolate Donut")
println(s"Elements of list1 = $list1")

You should see the following output when you run your Scala application in IntelliJ:


Step 1: How to initialize an immutable List with 3 elements
Elements of list1 = List(Plain Donut, Strawberry Donut, Chocolate Donut)

 

2. How to access elements of immutable List at specific index

The code below shows how to access elements of immutable List at specific index.


println("\nStep 2: How to access elements of immutable List at specific index")
println(s"Element at index 0 = ${list1(0)}")
println(s"Element at index 1 = ${list1(1)}")
println(s"Element at index 2 = ${list1(2)}")

You should see the following output when you run your Scala application in IntelliJ:


Step 2: How to access elements of immutable List at specific index
Element at index 0 = Plain Donut
Element at index 1 = Strawberry Donut
Element at index 2 = Chocolate Donut

 

3. How to append elements at the end of immutable List using :+

The code below shows how to append elements at the end of immutable List using :+


println("\nStep 3: How to append elements at the end of immutable List using :+")
val list2: List[String] = list1 :+ "Vanilla Donut"
println(s"Append elements at the end using :+ = $list2")

You should see the following output when you run your Scala application in IntelliJ:


Step 3: How to append elements at the end of immutable List using :+
Append elements at the end using :+ = List(Plain Donut, Strawberry Donut, Chocolate Donut, Vanilla Donut)

 

4. How to prepend elements at the front of immutable List using +:

The code below shows how to prepend elements at the front of immutable List using +:


println("\nStep 4: How to prepend elements at the front of immutable List using +:")
val list3: List[String] = "Vanilla Donut" +: list1
println(s"Prepend elements at the front using +: = $list3")

You should see the following output when you run your Scala application in IntelliJ:


Step 4: How to prepend elements at the front of immutable List using +:
Prepend elements at the front using +: = List(Vanilla Donut, Plain Donut, Strawberry Donut, Chocolate Donut)

 

5. How to add two immutable lists together using ::

The code below shows how to add two immutable lists together using ::


println("\nStep 5: How to add two immutable lists together using ::")
val list4: List[Any] = list1 :: list2
println(s"Add two lists together using :: = $list4")

You should see the following output when you run your Scala application in IntelliJ:


Step 5: How to add two immutable lists together using ::
Add two lists together using :: = List(List(Plain Donut, Strawberry Donut, Chocolate Donut), Plain Donut, Strawberry Donut, Chocolate Donut, Vanilla Donut)

NOTE:

  • Using :: returns a new List(List(...), elements from the second list)

6. How to add two immutable Lists together using :::

The code below shows how to add two immutable Lists together using :::


println("\nStep 6: How to add two immutable Lists together using :::")
val list5: List[String] = list1 ::: list2
println(s"Add two lists together using ::: = $list5")

You should see the following output when you run your Scala application in IntelliJ:


Step 6: How to add two immutable Lists together using :::
Add two lists together using ::: = List(Plain Donut, Strawberry Donut, Chocolate Donut, Plain Donut, Strawberry Donut, Chocolate Donut, Vanilla Donut)

 

7. How to initialize an empty immutable List

The code below shows how to initialize an empty immutable List.


println("\nStep 7: How to initialize an empty immutable List")
val emptyList: List[String] = List.empty[String]
println(s"Empty list = $emptyList")

You should see the following output when you run your Scala application in IntelliJ:


Step 7: How to initialize an empty immutable List
Empty list = List()

This concludes our tutorial on Learn How To Use Scala's Immutable List and I hope you've found it useful!

 

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Summary

In this tutorial, we went over the following:

  • How to initialize an immutable List with 3 elements
  • How to access elements of immutable List at specific index
  • How to append elements at the end of immutable List using :+
  • How to prepend elements at the front of immutable List using +:
  • How to add two immutable lists together using ::
  • How to add two immutable Lists together using :::
  • How to initialize an empty immutable List

Tip

Source Code

The source code is available on the allaboutscala GitHub repository.

 

What's Next

In the next tutorial, I will show you how to use Scala's Immutable ListSet.

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Nadim Bahadoor
Senior Software Developer | Elsevier
Founder of allaboutscala.com. I have over 10 years of experience in building large scale real-time trading systems in the financial industry. Passionate about Distributed Systems, Scala, Big Data and Functional Programming. Stay in touch for upcoming tutorials!
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