Convert one case class to another by using selected element

user_14634670 0
Viewed 114

Want to retrieve specific element from the input class while making the list of an output case class.

Example :

case class Student(id:Int, grade:Int, marks:Int)
case class StudentID(id:Int,grade:Int)


val inputList= Option[List(Student(1,100,234) ,Student(2,200,453), Student(3,300,556))]
val outputList=List(StudentID(1,100),StudentID(2,200),StudentID(3,300)) //result

I am trying to get only the id and grade. Please suggest. Also, the problem is input list is Option[].

val a = inputList.iterator.flatMap{ i=> outputList(i.map(_.id)) }
scala
3 Answers

The question is still not clear, but I think this is the code you want:

inputList.map(_.map(s => StudentID(s.id, s.grade))).getOrElse(Nil)

The outer map and getOrElse(Nil) deal with the fact that the input is an Option[List] not just List. The inner map converts each element of the input List from Student to StudentID.

user_76626700

If the transition from Student-to-StudentID occurs at multiple places throughout the code base, then it might make sense to put the translation logic in the companion object.

case class Student(id:Int, grade:Int, marks:Int)
case class StudentID(id:Int,grade:Int)
object StudentID {
  def apply(s: Student) = new StudentID(s.id, s.grade)
}

val inputList= 
  Option(List(Student(1,100,234) ,Student(2,200,453), Student(3,300,556)))

inputList.map(_.map(StudentID(_)))
//res0: Option[List[StudentID]] =
//  Some(List(StudentID(1,100), StudentID(2,200), StudentID(3,300)))
user_49931280

I'd suggest that you use any of the many available case class mapping libraries.

Some examples:

You could also write your own solution with shapeless or macros, but it's not worth it since there are already working solutions.

Example with chimney:

import io.scalaland.chimney.dsl._

inputList match {
  case Some(l) => l.map(s => s.into[StudentID].transform)
  case None => Nil
}

Alternatively, you could just manually map one case class to another, but it can get tedious with case classes with many fields.

user_13033240
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