Kotlin : filter & map (Post 19)

Hello All,

Today I am going to share 2 another important operations that are "filter" & "map" ,

Filter : This is used to apply a condition , on collections elements and get the resultant collections data , then there "filter" is used.

Map : This is used to transform all the elements of collections data

 override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
       
        var myList =  mutableListOf<Int>(34 , 6 , 29 , 15 , 65 , 9 , 12 , 42)
        var myEvenList = myList.filter { it%2 == 0 }
        for(num in myEvenList){
            println(num)
        }
         println("Double list : ")

        var myDoubleList = myEvenList.map { it*2 }
        for(num in myDoubleList){
            println(num)
        }
    }

Output :

34
6
12
42

Double list : 
68
12
24
84

Here , we can see that I have added the condition to get even number from the myList , which is returning myEvenList , then I applied the map condition for getting the double numbers of all the elements of myEvenList , which we are getting in myDoubleList .

Now take one example of Employee Data class :

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
     
        var myList = listOf<Employee>(
            Employee(101,"Alen"),
            Employee(102,"Harrey"),
            Employee(103,"John"),
            Employee(104,"Sam"),
            Employee(105,"Alice"))
        var nameList: List<String> = myList.map{it.empName}

        for(name in nameList){
            println(name)
        }
        println("Initial List : ")
        var initialList = nameList.filter{ person -> person.startsWith("A")}
        for(num in initialList){
            println(num)
        }
    }
    class Employee (var empId: Int, var empName: String) {
    }

Output :

Alen
Harrey
John
Sam
Alice

Initial List : 
Alen
Alice

Here I have used one list , which is containing the list of Employees ,
then in nameList , all the names are fetched using map()
then from nameList , all the names are fetched starting with 'A'  , returning the initialList .

Hope this will help to understand these two important topics of Kotlin. Will share another interesting topic in my next post , till then Happy Coding 😀😀