anybody knows a nicer way to do this: ``` val childUnitsById = units .map { ...

# getting-started

[jaspersmit]

anybody knows a nicer way to do this:

val childUnitsById = units
                .map { if(it.parent != null) it else null }
                .filterNotNull()
                .groupBy {it.parent!!}

[Andreas Sinz]

jaspersmit: use mapNotNull { }

[jaspersmit]

great that that exists:)

[jaspersmit]

so then we have

val childUnitsById = units
                .mapNotNull { if(it.parent != null) it else null }
                .groupBy {it.parent!!}

[jaspersmit]

No suggestions? 😛

[menegatti]

wasn't a good one haha

[jaspersmit]

thats unfortunate 😞

[menegatti]

but why do you need to map first?

[Andreas Sinz]

@jaspersmit is it correct that you are just filtering by parent != null and then group them together? you could do that with filter { it.parent != null } too

[menegatti]

exactly what I was thinking

[jaspersmit]

yes you're right but i was looking for something to avoid the !!

[jaspersmit]

but i was not very succesful with that

[menegatti]

ooh, yeah, I don't think there's a way to smart cast it

[jaspersmit]

i realize i need a groupByNotNull

[menegatti]

However I think this is a pretty-self contained case of the !! operator

[menegatti]

I'd go forward with this

[jaspersmit]

yes i will do that 🙂

[cedric]

The only way to get rid of !! would be to create a List<ParentType> (not nullable), so you'd have to generate that list first. Means you'd iterate twice, but you'd get rid of the !!.

[cedric]

If you know that list is small compared to the original list, probably worth doing. If not, your initial code is fine

[cedric]

Do keep in mind that technically, you can still get an NPE (i.e. if another thread sets one of these parents to null by the time you get there)

[jaspersmit]

luckily parent is immutable

[gjesse]

this seems to work fine for me, no !! needed

val childUnitsById = units
            .filter { it.parent != null }
            .groupBy { it.parent }

[cedric]

What's the type of it.parent?

[gjesse]

data class Node(val parent: Node?, val id: String) {
    override fun toString(): String {
        return "Node(id='$id')"
    }
}