Hello, World! What would be the easiest way to get an "inverted" version of a Map (by that I mean the values become the keys and vice versa)?

What would you do with duplicate values? Would a

Map<K, V>

->

Map<V, List<K>>

?

very good point. Didn't think of it because in my case it's a 1-1 mapping.

tbh I thought there was a built in operator, but this will do the trick, albeit a bit untidily:

map.entries
        .map { it.value to it.key }
        .groupBy { it.first }
        .mapValues { it.value.map { it.second } }

thanks! Isn't there a specific

.map

for Maps ? Something that takes a

(k: K1, v:V1) -> Pair<K2, V2>

and returns a

Map<K2, V2>

?

mapOf("A" to 1, "B" to 2, "C" to 3).map { it.value to it.key }.toMap()

should work for 1:1 maps

mapOf(...).entries.associateBy({ it.value }) { it.key }

should also work for 1:1 maps

Thanks a lot! Very nice

You could add a little sugar to it by creating an extension function on the

Map

interface if this is functionality you find yourself requiring often 🙂