Stream: beginners

Topic: List.flatten or List.flatMap

Scally (Dec 09 2024 at 17:05):

Am I mistaken or do these functions not exist? How would I go about doing things like that? Do I actually need to implement them myself?

Kilian Vounckx (Dec 09 2024 at 17:08):

I think you are looking for joinMap

Kilian Vounckx (Dec 09 2024 at 17:08):

And join instead of flatten

Scally (Dec 09 2024 at 17:12):

Ah cool, thanks. What about something like joinMapWithIndex?

Kilian Vounckx (Dec 09 2024 at 17:14):

As far as I know, it doesn't exists. I use mapWithIndex followed by join in that case. Slightly less performant, but it works

Kilian Vounckx (Dec 09 2024 at 17:15):

If you really want the full performance, you'd need to use walk(WithIndex) and allocate the buffer manually up front with List.withCapacity

Anthony Bullard (Dec 09 2024 at 17:57):

If you have fold(walk) you can build anything as my old CTO once told me

Last updated: Jul 26 2025 at 12:14 UTC