Hi I am having a map like this: [ key1 : [1,2,3], key2: [2,3,4], key3: [3,4,5]] I would like to get...

# announcements

[Jgafner]

Hi

I am having a map like this:
[ key1 : [1,2,3], key2: [2,3,4], key3: [3,4,5]]
I would like to get a map like this:
[1[key1],2[key1,key2],3[key1,key2,key3],4[key2,key3],5:[key3]]

any suggestions on how to group by elements in a list and not the list itself?
Thanks

[Lidonis Calhau]

Are you look for something like this ?

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

[Jgafner]

no this print:

{[1, 2, 3]=key1, [2, 3, 4]=key2, [3, 4, 5]=key3}

[Jgafner]

I want to have a map where I have each one of the single item in the values in the original map mapped to a list of keys where is appear

[Jgafner]

fun main() {
    val x = mapOf("key1" to listOf(1, 2, 3), "key2" to listOf(2, 3, 4), "key3" to listOf(3, 4, 5))

    val y = x.entries.associateBy({ it.value }) { it.key }
    println(y)
}

[Lidonis Calhau]

I think this does what you want but maybe there is better way 😅

x.entries.flatMap { e -> e.value.map { it to e.key } }.groupBy  ( { it.first }, { it.second })

[Jgafner]

Thanks @Lidonis Calhau it works 👑

[Pedro Pereira]

This solution should be more efficient because it doesn't create the intermediate list

val y = mutableMapOf<Int, MutableList<String>>()
x.entries.forEach { e -> e.value.forEach { y.getOrPut(it) { mutableListOf() }.add(e.key) } }

[Jgafner]

Thanks @Pedro Pereira will check that