Summary of ArrayList ordering in Kotlin (Android) - arrays

Question

I am trying to provide a summary of items within an ArrayList (where order matters). Basically, I am setting up an exercise plan with two different types of activities (Training and Assessment). I then will provide a summary of the plan after adding each training/assessment to it.
The structure I have is something along the lines of:
exercisePlan: [
{TRAINING OBJECT},
{TRAINING OBJECT},
{ASSESSMENT OBJECT},
{TRAINING OBJECT}
]
What I want to be able to do is summarise this in a format of:
2 x Training, 1 x Assessment, 1 x Training, which will be displayed in a TextView in a Fragment. So I will have an arbitrarily long string that details the structure and order of the exercise plan.
I have tried to investigate using a HashMap or a plain ArrayList, but it seems pretty messy so I'm looking for a much cleaner way (perhaps a MutableList). Thanks in advance!

Answer 1

ArrayList is just a specific type of MutableList. It's usually preferable to use a plain List, because mutability can make code a little more complex to work with and keep robust.
I'd create a list of some class that wraps an action and the number of consecutive times to do it.
enum class Activity {
Training, Assessment
}
data class SummaryPlanStep(val activity: Activity, val consecutiveTimes: Int) {
override fun toString() = "$consecutiveTimes x $activity"
}
If you want to start with your summary, you can create it and later convert it to a plain list of activities like this:
val summary: List<SummaryPlanStep> = listOf(
SummaryPlanStep(Activity.Training, 2),
SummaryPlanStep(Activity.Assessment, 1),
SummaryPlanStep(Activity.Training, 1),
)
val plan: List<Activity> = summary.flatMap { List(it.consecutiveTimes) { _ -> it.activity } }
If you want to do it the other way around, it's more involved because I don't think there's a built-in way to group consecutive duplicate elements. You could a write a function for that.
fun <T> List<T>.groupConsecutiveDuplicates(): List<Pair<T, Int>> {
if (isEmpty()) return emptyList()
val outList = mutableListOf<Pair<T, Int>>()
var current = first() to 1
for (i in 1 until size) {
val item = this[i]
current = if (item == current.first)
current.first to (current.second + 1)
else {
outList.add(current)
item to 1
}
}
outList.add(current)
return outList
}
val plan: List<Activity> = listOf(
Activity.Training,
Activity.Training,
Activity.Assessment,
Activity.Training
)
val summary: List<SummaryPlanStep> = plan.groupConsecutiveDuplicates().map { SummaryPlanStep(it.first, it.second) }

Answer 2

This is what I have set up to work for me at the moment:
if (exercisePlanSummary.isNotEmpty() && exercisePlanSummary[exercisePlanSummary.size - 1].containsKey(trainingAssessment)) {
exercisePlanSummary[exercisePlanSummary.size - 1][trainingAssessment] = exercisePlanSummary[exercisePlanSummary.size - 1][trainingAssessment]!! + 1
} else {
exercisePlanSummary.add(hashMapOf(trainingAssessment to 1))
}
var textToDisplay = ""
exercisePlanSummary.forEach {
textToDisplay = if (textToDisplay.isNotEmpty()) {
textToDisplay.plus(", ${it.values.toList()[0]} x ${it.keys.toList()[0].capitalize()}")
} else {
textToDisplay.plus("${it.values.toList()[0]} x ${it.keys.toList()[0].capitalize()}")
}
}
where trainingAssessment is a String of "training" or "assessment". exercisePlanSummary is a ArrayList<HashMap<String, Int>>.
What #Tenfour04 has written above is perhaps more appropriate, and a cleaner way of implementing this. But my method is quite simple.