Transform Map Values to Data Class in Kotlin - kotlin

Question

I have a map whose values are an arraylist of different object types (LocalDate, LocalTime, Float, List(Float)).
I would like to transform the map values to a custom data class i have created.
I have tried destructuring the maps value components however i am getting error "Destructuring declaration initializer of type Map.Entry<String, Any> must have a 'component3()' function".
How would i perform this transformation below?
Blockquote
val localDate1 = LocalDate.now()
val localTime1 = LocalTime.now()
val float1 = 1f
val floatList1 = listOf<Float>(1f, 2f, 3f)
val localDate2 = LocalDate.now()
val localTime2 = LocalTime.now()
val float2 = 2f
val floatList2 = listOf<Float>(4f, 5f, 6f)
val myMap = HashMap<String, Any>()
myMap["keyOne"] = arrayListOf<Any>(localDate1, localTime1, float1, floatList1)
myMap["keyTwo"] = arrayListOf<Any>(localDate2, localTime2, float2, floatList2)
val newMap = myMap.mapValues { (date, time, float, floatList) -> /*Here i am getting destructuring error*/
CustomObject(
date,
time,
float,
floatList
)
}
Blockquote
data class CustomObject (
val date: LocalDate,
val time: LocalTime,
val float: Float,
val floatList: List<Float>
)

Answer 1

Map.mapValues() takes a lambda whose receiver is the map Entry, not its value.  (The method is named for the lambda's results, not its parameter.) So you can't destructure it that way.
There are also typecasting issues: myMap is a map whose values are Any, but you seem to be assuming that each value is actually a List of Any (with the actual elements being of the appropriate types in the appropriate order). So you need to do the necessary casting to tell the compiler what types they are (or at least, what types you assume they are…)
So you could destructure it as a separate step, e.g.:
val newMap = myMap.mapValues { entry ->
val (date, time, float, floatList) = entry.value as List<Any>
CustomObject(
date as LocalDate,
time as LocalTime,
float as Float,
floatList as List<Float>
)
}
Or you could just use the array values directly:
val newMap = (myMap as Map<String, List<Any>>).mapValues {
CustomObject(
it.value[0] as LocalDate,
it.value[1] as LocalTime,
it.value[2] as Float,
it.value[3] as List<Float>
)
}
However I think it would be a lot better to avoid having the lists in the first place. You're taking a lot of extra code to create the lists and then convert them — but much of that code is unsafe: each destructuring can fail with an exception (perhaps ArrayIndexOutOfBoundsException) if the list isn't long enough, and each cast can fail with a ClassCastException. Casts are always a code smell, especially unchecked ones like these; Kotlin's type system is powerful enough to express most things you're likely to want, so bypassing it like this tends to indicate that the design can be improved.
So if there's any way you can create your custom objects directly, that's likely to be shorter, safer, faster, and easier to read.

Answer 2

import java.time.LocalDate
import java.time.LocalTime
data class CustomObject(
val date: LocalDate,
val time: LocalTime,
val float: Float,
val floatList: List<Float>
)
val myMap = mapOf(
"keyOne" to listOf(LocalDate.now(), LocalTime.now(), 1f, listOf(1f, 2f, 3f)),
"keyTwo" to listOf(LocalDate.now(), LocalTime.now(), 2f, listOf(4f, 5f, 6f))
)
val newMap = myMap.mapValues {
CustomObject(
it.value[0] as LocalDate,
it.value[1] as LocalTime,
it.value[2] as Float,
(it.value[3] as List<*>).map { fl -> fl as Float }
)
}
println(newMap)