Adding BigDecimal Numbers in Kotlin

I have the following mapping, but now I need to add percentage data to the list, so to create the formula, I need the total of all the values in the list

data class Data(
  val id: Int,
  val cost: Int,
  val env: String,
  val item: String
)

data class TotalCost(
  val item: String,
  val env: String,
  val cost: BigDecimal
)

val input = listOf(
  Data(id = 1, cost = 0.00000000001, env = "prod", item = "Storage"),
  Data(id = 2, cost = 0.00000000002, env = "qa", item = "Storage"),
  Data(id = 3, cost = 0.00000000003, env = "prod", item = "Storage"),

  Data(id = 4, cost = 0.00000000005, env = "qa", item = "Bandwidth"),
  Data(id = 5, cost = 0.00000000002, env = "qa", item = "Bandwidth"),
  Data(id = 6, cost = 0.00000000005, env = "prod", item = "Bandwidth"),
  Data(id = 7, cost = 0.00000000006, env = "prod", item = "Bandwidth"),
  Data(id = 8, cost = 0.00000000001, env = "prod", item = "Bandwidth"),

  Data(id = 9, cost = 0.00000000005, env = "qa", item = "vm"),
  Data(id = 10, cost = 0.00000000002, env = "uat", item = "vm"),
  Data(id = 11, cost = 0.00000000003, env = "qa", item = "vm"),
  Data(id = 12, cost = 0.00000000004, env = "prod", item = "vm"),
  Data(id = 13, cost = 0.00000000005, env = "uat", item = "vm")
)

val result = input
  .groupBy { 
    it.item to it.env 
  }
  .map { (key, value) ->
    listOf(
      key.first,
      key.second,
      value.sumOf { it.cost.toBigDecimal() }
    )

}

I am trying this;

 var totalCost: BigDecimal = BigDecimal.ZERO

 result.forEach { totalCostData ->
     totalCost = totalCost.add(totalCostData[2].toBigDecimal())
 }

and getting this error message;

 Unresolved reference. None of the following candidates is applicable because of receiver type mismatch: 

>Solution :

Problem is located here:

listOf(
    key.first,
    key.second,
    value.sumOf { it.cost.toBigDecimal() }
)

You needed to transform items into 3 distinct values, so you stored them in a list. However, first two values are strings and the third is BigDecimal. List can only store items of same types, so in this case it becomes pretty much List<Any> and then totalCostData[2] is just Any (this is not exactly correct).

There are two ways to fix the problem. You can either cast it to BigDecimal as we know its type:

totalCost = totalCost.add(totalCostData[2] as BigDecimal)

Or better, do not use a list, but store results in a custom and fully typed class. As a matter of fact, it seems you already created such class, but for some reason you didn’t use it:

TotalCost(
    key.first,
    key.second,
    value.sumOf { it.cost.toBigDecimal() }
)

...

totalCost = totalCost.add(totalCostData.cost)