How To Create A List In Scala

Scala List

Definition of Scala List

Scala list is immutable which means once assign object cannot change itself. List is also a part of the collection that is used to store and retrieve elements. List in scala is some like array which store elements of the same type only. Scala list internally uses a linked list and as we know the linked list is better suited for manipulation operation. It is based on linked List data structure and immutable in nature which means object once assign cannot change it, they maintain the insertion order as well and come up with a various method which enhance working with a list, they are the part of the collection in Scala only.

Syntax of Scala List

In Scala, we can create a list in two ways

We can assign value to the list while creating the list object without defining the data type. We can also create a list with data type declaration with it so only that type of data we can assign to a specific list later.

valvariable_name: List[data_type] = List(element1, element2 element3, element4)

and

valvariable_name = List(element1, element2 element3, element4)

In the above syntax, we have two ways to declare or create the list object.

Example:

val list1: List[Int] = List(100, 200, 300, 400, 500)

and

val list2 = List("hello", "hello 2", "hello3 ", "so on..")

How does List Work in Scala?

List is used to store elements. These elements has to be of the same type only. In Scala list represent the linked list data structure. We can discuss the linked list of how it works;

In a singly linked list structure, we have a node which contained two things data and address to the next node see in below example. we can modify the values present inside the Scala list programmatically through our logic. Also, the list can contain duplicate elements in it and maintain the insertion order as well. It is defined inside scala.collection.immutable package. We can have a look for its supertype and subclasses.

Superclasses ;

DefaultSerializable	StrictOptimizSeqOps	LinearSeq	LinearSeqOps	AbstractSeq
Iterable	AbstractIterable	Seq	SeqOps	PartialFunction
IterableactoryDefaults	IterableOps	IterableOnceOps	AnyRef	Any

The Scala list offers various methods. Few are described below;

Method Name	Return Type
sortBy	List
sortWith	List
Sum	Sum of all values in the list
++	List
+	List

Scala list hierarchy;

AbstarctSeq
LinearSeq
LinerSeqOps
StrictOptimizedLinearSeqOps
StrictOptimizedSeqOps
IterableFactoryDefaults
UnliftOps

We should keep in mind the below points while working with Scala list;

It is immutable and it is defined under scala.collection.immutable package.
The Scala list is based on a linked list data structure.
It provides us various methods to deal with the list.
Data present insideScala list should be of the same type only.

Method and Examples of Scala List

Following are the list of methods and examples as given below:

1. for()

This method is just we are using to print the list element of different types. see below;

Example

import scala.collection.immutable._ object Main extends App{ // Your code here! val list1: List[Int] = List(100, 200, 300, 400 , 500) val list2 = List("initilize here", "hello1", "hello2", "hello3", "so on .....") println("values inside first list are :: ") println(list1) // output println("values inside second list are :: ") for(value<-list2) { println("value is :: " +value) } }

Output:

Scala List-1.1

2. ++

This method return a new list that contains all the elements from both the list.

Example

import scala.collection.immutable._ object Main extends App{ // Your code here! val list1: List[Int] = List(100, 200, 300, 400, 500) val list2: List[Int] = List(800, 900, 1500, 1700, 300) println("values inside first list are :: ") println(list1) println("values inside second list are :: ") println(list2) // applying function val result = list1 ++ list2 println("result is ::: " + result) }

Output:

Scala List-1.2

3. head

This method will return the first element of the list.

Example

Output:

Scala List-1.3

4. tail

This method returns a list which contains all element but not the first element.

Example

Output:

Scala List-1.4

5. Empty

This method check list is empty or not and returns true or false based on the result.

Example

import scala.collection.immutable._ object Main extends App{ // Your code here val list1: List[Int] = List(100, 200, 300, 400, 500) val list2: List[Int] = List(800, 900, 1500, 1700, 300) println("values inside first list are :: ") println(list1) println("values inside second list are :: ") println(list2) // applying function val result = list1.empty println("result is ::: " + result) }

Output:

Output-1.5

6. Concat

This method is used to concate two list and returns a new list.

Example

import scala.collection.immutable._ object Main extends App{ // Your code here! val list1: List[Int] = List(100, 200, 300, 400, 500) val list2: List[Int] = List(800, 900, 1500, 1700, 300) println("values inside first list are :: ") println(list1) println("values inside second list are :: ") println(list2) // applying function val result = List.concat(list1 , list2) println("result is ::: " + result) }

Output:

Output-1.6

7. reverse

This will reverse the list element and print them from the end.

Example

Output:

Output-1.7

8. indexOf()

This method returns the index of elements.

Example

import scala.collection.immutable._ object Main extends App{ // Your code here! val list1: List[Int] = List(100, 200, 300, 400, 500) val list2: List[Int] = List(800, 900, 1500, 1700, 300) println("values inside first list are :: ") println(list1) // applying function val result = list1.indexOf(300) println("result is ::: " + result) }

Output:

Output-1.8

Conclusion

It based on the linked List data structure. Where the array is flat. It is immutable also. List is also used to store and retrieving of the element. It maintains the insertion order that means in which order we have added can be obtained in the same sequence.