转换不可变 kolin 的更好方法 Map<k,v></k,v>

Question

I have a nested immutable kotlin Map<K, Map<K,V>> which I would like to loop through each entry and perform some transformation and produce a new Map<K, Map<K,V>> which transformed key, values.

Here is my current solution but I feel like there would be a better way to achieve this.

fun main() {
    // I would like to loop through each key,value pair and transform them and produce a new map with transformed values.
    val mapToTransform = mapOf(1 to mapOf("one" to "I"), 2 to mapOf("two" to "II"))
    
    // Here is my current solution to achieve it. Is there any better way to do this?
    val transformedMap = mapToTransform.map { (outerMapKey, innerMap) -> 
        outerMapKey+1 to innerMap.map { (innerMapKey, innerMapValue) ->
            innerMapKey.uppercase() to "$innerMapValue is Roman letter"
        }.toMap()
    }.toMap()
    
    println(transformedMap)
}

Answer 1

First, I should say that I think your current code is perfectly fine and readable. I would not change it. However, since you don't seem to like using toMap or creating pairs,

I feel instead of creating pairs and using.toMap() twice there should be a cleaner way.

It is possible to not use toMap or create pairs by repeatedly mapKeys and mapValues :

val transformed = mapToTransform
    .mapKeys { (outerMapKey, _) -> outerMapKey + 1}
    .mapValues { (_, innerMap) ->
        innerMap
            .mapKeys { (innerKey, _) -> innerKey.uppercase() }
            .mapValues { (_, innerValue) -> "$innerValue is Roman letter" }
    }

This might be a little more readable depending on who you ask. On the other hand, it creates a lot of intermediate Map s. I'm not sure about how the performance of this compares to your original code, but it probably depends on the contents of the map itself.