Kotlin convert csv to map <String, List>-CodePudding

I have following CSV

US;Americas
CA;Americas
FR;Europe
CH;Asia
...

I want to have Map of -> String, List, is it possible to achieve this via associate, or something else ?

So far I have this:

csv.split("\n").associate { 
  val (code, region) = it.split(";") 
  region to code 
}

but this is just mapping the region to only one code, also tried

region to listOf(code)

expected result:

Americas -> US, CA, BR ...
Europe -> FR, IT, CH ...
Asia -> CH, JP, KR ...

CodePudding user response：

csv.split("\n").groupBy({ it.substringAfter(";") }) { it.substringBefore(";") }})

CodePudding user response：

associate would replace the value if the key already iterated. You can instead use groupBy to specify key and value for the map

csv.split("\n").map {
    val (code, region) = it.split(";")
    region to code
}.groupBy({ it.first }) { it.second }

CodePudding user response：

Alternatively to sidgate's excellent answer you could also do

csv.split("\n").groupBy({
    it.split(";")[1]
}){
    it.split(";")[0]
}

It avoids having to create a map first, but calls split more often. I'm not sure what would be better in terms of speed/efficiency.