Kotlin duplicate items in list to create a new list of different objects with the same data

Question

I have two data structures:

data class MyObjectA(val foo: String, val barA: String, val barB: String)
data class MyObjectB(val foo: String, val bar: String)

And I have a list with MyObjectA items:

val mylistA = listOf(
    MyObjectA("aaa", "bbb", "ccc"), 
    MyObjectA("ddd", "eee", "fff")
)

I want to get a list with each object repeated, but each new item containing only some of the original data:

val mylistB = listOf(
    MyObjectB("aaa", "bbb"),
    MyObjectB("aaa", "ccc"),
    MyObjectB("ddd", "eee"), 
    MyObjectB("ddd", "fff")
)

Is there some extension function in Kotlin to do it in short?

Answer 1

I would do it like this:

data class MyObjectA(val foo: String, val barA: String, val barB: String) {
    fun toB() = listOf(MyObjectB(foo, barA), MyObjectB(foo, barB))
}
data class MyObjectB(val foo: String, val bar: String)

fun main() {
    val mylistA = listOf(
        MyObjectA("aaa", "bbb", "ccc"),
        MyObjectA("ddd", "eee", "fff")
    )

    val myListB = mylistA.flatMap { it.toB() }

    println(myListB)
}

If you don't want to add the toB() function to the data class you can of course also do it directly like

val myListB = mylistA.flatMap { listOf(MyObjectB(it.foo, it.barA), MyObjectB(it.foo, it.barB)) }