How do i add all values with the same year in list?

TrueCode :

I have a list of strings that looks something like this :

• 2010 1 11.45
• 2010 2 09.50
• 2010 3 15.00
• .
• .
• .
• 2019 12 11.10

(the list is a list of spends per month between the years of 2010 - 2019)

I have separated the list into 3 lists for each value such as :

for(....){

val part = list.get(i).split(" ")
val year = parts[0]
val month = parts[1]
val spend = parts[2]

yearlist.add(year)
monthlist.add(month)
spendlist.add(spend)
}

Now my issue is that I want to find the year with the highest spend total. How would I add all of the spends for each year?

I have tried the following method however this gives me an IndexOutOfBounds Exception:

var totalspend = 0
for(i in 0..yearlist.size-1){

if(yearlist[i]==yearlist[i+1]){//i get an error here 
    totalspend = totalspend + spendlift[i]
}
else if(yearlist[i]!=yearlist[i+1]){
    totalspend = totalspend + spendlift[i]
    spendforyear.add(totals(year[i], totalspend))
    totalspend = 0.0
}

}

I assume the error is because i cant compare the final yearlist value with yearlist[i+1] as i+1 is out of bounds.

How would i go about solving this?

Mohamed Mohsin :

I would suggest saving the year, month and spend in a data class and then use collection functions:

data class Report(val year: String, val month: String, val spend: Double)

fun main() {

    val reports = listOf(
        Report("2010", "1", 11.45),
        Report("2010", "2", 09.50),
        Report("2010", "3", 15.00),
        Report("2019", "12", 11.10)
    )
    val groupedReports = reports.groupBy { it.year }
    val mostSpending = groupedReports.maxBy { it.value.sumByDouble { report -> report.spend } }
    println(mostSpending?.key) // year with the most spending
    println(mostSpending?.value?.sumByDouble { it.spend }) // the spending on that year
}