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Scala Lists
  • Last Updated : 14 Mar, 2019

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:

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// 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)
        }
    }
}

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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:

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// 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)
    }
}

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Output:

The empty list is:
List()

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

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// 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)
    }
}

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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:

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    // 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)
        }
    }    
         

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    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:

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    // 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)
        }
    }

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    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:

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    // 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)
        }
    }    

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    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:

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// 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)
    }
}    

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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:

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// 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)
    }
}
  

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Output:

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