Scala Lists

A list is a collection which contains immutable data. List represents linked list in Scala. The Scala List class holds a sequenced, linear list of items.
Following are the point of difference between lists and array in Scala:

• Lists are immutable whereas arrays are mutable in Scala.
• Lists represents a linked list whereas arrays are flat.

Syntax:

val variable_name: List[type] = List(item1, item2, item3)
or
val variable_name = List(item1, item2, item3)

Some important points about list in Scala:

• In a Scala list, each element must be of the same type.
• The implementation of lists uses mutable state internally during construction.
• In Scala, list is defined under scala.collection.immutable package.
• A List has various methods to add, prepend, max, min, etc. to enhance the usage of list.

Example:

// Scala program to print immutable lists
import scala.collection.immutable._

// Creating object
object GFG
{
    // Main method
    def main(args:Array[String])
    {
        // Creating and initializing immutable lists
        val mylist1: List[String] = List("Geeks", "GFG",
                            "GeeksforGeeks", "Geek123")
        val mylist2 = List("C", "C#", "Java", "Scala",
                                        "PHP", "Ruby")

        // Display the value of mylist1
        println("List 1:")
        println(mylist1)

        // Display the value of mylist2 using for loop
        println("\nList 2:")
        for(mylist<-mylist2)
        {
            println(mylist)
        }
    }
}

Output:

List 1:
List(Geeks, GFG, GeeksforGeeks, Geek123)

List 2:
C
C#
Java
Scala
PHP
Ruby

In above example simply we are printing two lists.
Example:

// Scala program to illustrate the
// use of empty list
import scala.collection.immutable._

// Creating object
object GFG
{
    // Main method
    def main(args:Array[String])
    {

        // Creating an Empty List.
        val emptylist: List[Nothing] = List()
        println("The empty list is:")
        println(emptylist)
    }
}

Output:

The empty list is:
List()

Above example shows that the list is empty or not.
Example:

// Scala program to illustrate the
// use of two dimensional list
import scala.collection.immutable._

// Creating object
object GFG
{
    // Main method
    def main(args:Array[String])
    {
        // Creating a two-dimensional List.
        val twodlist: List[List[Int]] =
        List(
            List(1, 0, 0),
            List(0, 1, 0),
            List(0, 0, 1)
            )
        println("The two dimensional list is:")
        println(twodlist)
    }
}

Output:

The two dimensional list is:
List(List(1, 0, 0), List(0, 1, 0), List(0, 0, 1))

Basic Operations on Lists

The following are the three basic operations which can be performed on list in scala:

1. head: The first element of a list returned by head method.
   Syntax:

   list.head //returns head of the list
   

   Example:

   // Scala program of a list to
   // perform head operation
   import scala.collection.immutable._
   
   // Creating object
   object GFG
   {
       // Main method
       def main(args:Array[String])
       {
           // Creating a List.
           val mylist = List("C", "C#", "Java", "Scala",
                                       "PHP", "Ruby")
           println("The head of the list is:")
           println(mylist.head)
       }
   }
   
   Output:

   The head of the list is:
   C
   

2. tail: This method returns a list consisting of all elements except the first.
   Syntax:

   list.tail //returns a list consisting of all elements except the first
   

   Example:

   // Scala program to perform
   // tail operation of a list
   import scala.collection.immutable._
   
   // Creating object
   object GFG
   {
       // Main method
       def main(args:Array[String])
       {
           // Creating a List.
           val mylist = List("C", "C#", "Java", "Scala",
                                       "PHP", "Ruby")
           println("The tail of the list is:")
           println(mylist.tail)
       }
   }
   Output:

   The tail of the list is:
   List(C#, Java, Scala, PHP, Ruby)
   

3. isEmpty: This method returns true if the list is empty otherwise false.
   Syntax:

   list.isEmpty //returns true if the list is empty otherwise false.
   

   Example:

   // Scala program to perform
   // isEmpty operation of a list
   import scala.collection.immutable._
   
   // Creating object
   object GFG
   {
       // Main method
       def main(args:Array[String])
       {
   
           // Creating a List.
           val mylist = List("C", "C#", "Java", "Scala",
                                        "PHP", "Ruby")
           println("List is empty or not:")
           println(mylist.isEmpty)
       }
   }
   Output:

   List is empty or not:
   false
   

How to create a uniform list in Scala

Uniform List can be created in Scala using List.fill() method. List.fill() method creates a list and fills it with zero or more copies of an element.
Syntax:

List.fill() //used to create uniform list in Scala 

Example:

// Scala program to creating a uniform list
import scala.collection.immutable._

// Creating object
object GFG
{
    // Main method
    def main(args:Array[String])
    {
        // Repeats Scala three times.
        val programminglanguage = List.fill(3)("Scala")
        println( "Programming Language : " + programminglanguage )

        // Repeats 2, 10 times.
        val number= List.fill(8)(4)
        println("number : " + number)
    }
}

Output:

Programming Language : List(Scala, Scala, Scala)
number : List(4, 4, 4, 4, 4, 4, 4, 4)

Reversing List Order in Scala

The list order can be reversed in Scala using List.reverse method. List.reverse method can be used to reverse all elements of the list.
Syntax:

list.reverse //used to reverse list in Scala 

Example:

// Scala program of reversing a list order
import scala.collection.immutable._

// Creating object
object GFG
{
    // Main method
    def main(args:Array[String])
    {
        val mylist = List(1, 2, 3, 4, 5)
        println("Original list:" + mylist)

        // reversing a list
        println("Reverse list:" + mylist.reverse)
    }
}

Output:

Original list:List(1, 2, 3, 4, 5)
Reverse list:List(5, 4, 3, 2, 1)