Create a Map of Map of Object from a given List of Object-CodePudding

The structure of data class

data class ProductDetail(
  val name: String,
  val price: Int,
  val status: Status,
  val images: Images
...
)

I have a List<ProductDetail> and I want to convert it to Map<String, Map<Int, ProductDetail>>.

I tried looking into associate and associatedTo but I am only able to create Map<String, Pair<Int, ProductDetail>>. Is there a way to do this without the use to a loop in Kotlin?

CodePudding user response：

val mapOfMaps = list.groupBy(ProductDetail::name) // or { it.name }
    .mapValues { (name, productDetailsList) ->
        productDetailsList.groupBy(ProductDetail::price) // or { it.price }
    }

Use groupBy to easily create a map that groups items into matching lists. Then you can map those lists into inner maps with another groupBy call.

I am guessing associate is not the behavior you wanted here, because then every inner map would only contain one item, instead of all items with the matching name, and all repeated names would be dropped from the data.