Kotlin: groupBy and convert to other object - kotlin

Question

I have a list of objects
data class OldFormat(ShiftId: Int, NozzleValue: Int, NozzleId: Int , UserId: Int)
which I want to group by two of fields "shiftId and userId" and then subtract the maximum value of each group from the minimum value of the same group and then
sum the result and then convert it to a new object with this class:
data class NewFormat(ShiftId: Int, NozzleValue: Int, UserId: Int)
The process would be like this:
listOfOldFormat -> groupby(shiftId, userId) -> sum(maximumValue-minimumValue) -> listOfNewFormat

Answer 1

We do have groupBy function, so we have everything we need to.
I am not sure what do you mean by subtract the maximum value of each group from the minimum value of the same group and then sum the result (what should I sum?), so I did it as group.value.max - group.value.min and it's nozzeValue for NewFormat.
Code snippet:
data class OldFormat(val shiftId: Int, val nozzleValue: Int, val nozzleId: Int, val userId: Int)
data class NewFormat(val shiftId: Int, val nozzleValue: Int, val userId: Int)
fun main() {
val old = listOf(
OldFormat(0, 10, 10, 0),
OldFormat(0, 120, 10, 1),
OldFormat(1, 11, 8, 10),
OldFormat(0, 10, 1, 1),
OldFormat(1, 50, 10, 10)
) // Example data
old.groupBy {
it.shiftId to it.userId // After it we have Map<Key, List<OldFormat>>, where key is pair of shiftId and userId
}.map { entry ->
val max = entry.value.maxBy { it.nozzleValue }?.nozzleValue ?: 0
val min = entry.value.minBy { it.nozzleValue }?.nozzleValue ?: 0
entry.key to (max - min) // Just do whatever you want with that data
}.map {
NewFormat(
shiftId = it.first.first,
userId = it.first.second,
nozzleValue = it.second
) // And now map it into type you want
}.let {
println(it) // Just for seeing result
}
}