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Scala Trait Traversable | Set-1

  • Last Updated : 12 Apr, 2019

Introduction:
A root trait of the entire class of the Scala collections is Trait Traversable. It is available at the uppermost position of the collection hierarchy. It has uniquely one abstract operation, which is foreach. Here each of the operations are assured to be executed in a single-threaded approach.
Syntax:

def foreach[U](f: Elem => U)

Here, the operation f is concerned with all the elements of the collection and Elem => U is the type of operation, where “Elem” is the type of elements in the Scala’s collection and “U” is an inconsistent result type.

Some Important points:

  • Traversable is accomplished by the Scala’s Collection classes.
  • It is obligatory for Traversable to define foreach method only, as Traversable can inherit all the other methods.
  • The foreach method could traverse all the elements of the Scala’s collection class.
  • There are numerous concrete methods which are defined by Traversables.
  • List, Array, Map, Set, and many more are the subclass of Traversables.
Operations performed by the Class Traversable are as follows:
  1. Abstract Method:
    The only abstract method here is foreach, which can traverse over all the elements of the Collection.
    Example :




    //Scala program of abstract method
      
    //Creating object 
    object CS 
    {
        //Main method
        def main(args: Array[String]) 
        {
            //Creating an Array of elements
            val x = Array("GEEKS", "FOR", "GEEKS")
      
            //Calling foreach method
            x.foreach { E =>
            val y = E.toLowerCase
      
            //Display strings
            println(y)
            }
        }
    }
    Output:



    geeks
    for
    geeks
    

    Here, all the elements of the Array stated above are traversed by foreach method and then they are converted from uppercase to lowercase.
    Example:




    // Scala program of abstract method
      
    // Creating object 
    object GFG
    {
        // Main method
        def main(args: Array[String]) 
        {
            //Creating list of numbers
            val l = List(2, 6, 8, 7, 10, 11, 13)
      
            //Calling foreach and displaying
            //numbers of list after 
            //multiplication each of them
            l.foreach(n => println(n * 6))
        }
    }
    Output:
    12
    36
    48
    42
    60
    66
    78
    

    Here, foreach method traverses all the numbers of the list and multiplies each of them.

  2. Addition operation:
    Here, Addition operation i.e, ++ adds two Traversables together or adds each of the elements of an iterator to a Traversable.
    Example:




    // Scala program of addition operation
      
    // Creating object 
    object GFG
    {
        // Main method
        def main(args: Array[String]) 
        {
            // Creating set of numbers
            val x = Set(7, 8, 9, 10)
      
            // Creating list of numbers
            val y = List(1, 5, 8, 18)
      
            //performing addition operation
            val s1 = x ++ y
            val s2 = y ++ x
      
            //Displaying set
            println(s1)
      
            //Displaying list 
            println(s2)
        }
    }
    Output:
    Set(5, 10, 1, 9, 7, 18, 8)
    List(1, 5, 8, 18, 7, 8, 9, 10)
    

    Here, when a Set is added to a List then a Set is generated and when a List is added to a Set then a List is generated.

  3. Map operations:
    The three Map operations are map, flatMap, and collect.
    These Map operations create a new collection by assigning a few function to the elements of Scala collection.
    Example :




    // Scala program of Map operations
      
    // Creating object 
    object GFG
    {
      
        // Main method
        def main(args: Array[String]) 
        {
      
            // Creating Set of numbers
            val x = Set(8, 9, 5, 10)
      
            // Applying map operation
            val y = x.map(_ * 9)
      
            // Displaying Set 
            println(y)
        }
    }
    Output:
    Set(72, 81, 45, 90)
    

    Here, the Map operation (i.e, map) will assign the stated function on each elements of a Traversable and will return a new collection as output.
    Example :




    // Scala program of Map operations
      
    // Creating object 
    object GFG
    {
      
        // Main method
        def main(args: Array[String]) 
        {
      
            // Creating a List of lists
            val q = List(List(7), List(8, 9, 10), List(11, 12, 13))
      
            // Applying map operation
            val r = q.flatMap(_.map(_ + 3))
      
            // Displaying List
            println(r)
        }
    }
    Output:
    List(10, 11, 12, 13, 14, 15, 16)
    

    Here, the flatMap will assign the stated function on each elements within the elements and then will Concatenate the output.
    Example :




    // Scala program of Map operations
      
    // Creating object 
    object GFG
    {
      
        // Main method
        def main(args: Array[String]) 
        {
      
            // Creating List of numbers
            val x = List(9, 3, 5, 11, 15, 4)
      
            // Applying map operation 
            val y = x.collect 
            {
      
                // Partial function
                case z : Int if (z % 3 == 0) => z + 2
            }
      
            //Displaying list
            println(y)
        }
    }
    Output:
    List(11, 5, 17)
    

    Here, collect will assign a partial function to each elements of Traversable and will give a non-identical collection as output.




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