Kotlin convert csv to map <String, List>

Question

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 ...

Be careful with solutions that "simply" split by ;. If the country name has a ; escaped, the simple solution will cut the field with the ;. — AlikElzin-kilaka
– AlikElzin-kilaka, Commented Jun 29, 2022 at 6:40

lukas.j · Accepted Answer · 2021-12-09 20:58:58Z

4

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

answered Dec 7, 2021 at 12:52

lukas.j

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Comments

sidgate · Accepted Answer · 2021-12-07 12:35:16Z

3

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 }

answered Dec 7, 2021 at 12:27

sidgate

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Ivo · Accepted Answer · 2021-12-07 12:52:02Z

2

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.

answered Dec 7, 2021 at 12:52

Ivo

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