The most efficient solution for finding the minimum value

Question

I have a list of Sugar. The Sugar class has two field: price and weight:

data class Sugar(var price: Double, var weight: Double)

And I need to find max/min value by this fields. I found two ways to do this. The first way is to use a ready-made solution:

        val minPrice = list.minBy { it.price }?.price
        val maxPrice = list.maxBy { it.price }?.price

        val minWeight = list.minBy { it.weight }?.weight
        val maxWeight = list.maxBy { it.weight }?.weight

Second way:

        var minPrice = list.first().price
        var maxPrice = list.first().price

        var minWeight = list.first().weight
        var maxWeight = list.first().weight

        for (i in 1..list.size) {
            if (list[i].price < minPrice) {
                minPrice = list[i].price
            }
            if (list[i].price > maxPrice) {
                maxPrice = list[i].price
            }
            if (list[i].weight < minWeight) {
                minWeight = list[i].weight
            }
            if (list[i].weight > maxWeight) {
                maxWeight = list[i].weight
            }
        }

Both solutions work, but I need to find the most efficient one. Please, tell me which method is better to use, or perhaps there is a more efficient solution for this purpose.

Answer 1

Obviously the first solution iterates over the list for four times, while the second one iterates only once. So second option is performant. You can rewrite the solution in functional way

data class Metrics(val minPrice: Double = 0.0, val maxPrice: Double = 0.0, val minWeight: Double = 0.0, val maxWeight: Double = 0.0)

val (minPrice, maxPrice, minWeight, maxWeight) = list.fold(Metrics()){ acc, sugar ->
    Metrics(
      minPrice = min(sugar.price, acc.minPrice),
      maxPrice = max(sugar.price, acc.maxPrice),
      minWeight = min(sugar.weight, acc.minWeight),
      maxWeight = max(sugar.weight, acc.maxWeight)
    )
  }