```data class Comment(...) data class Post(val comments: List<Comment>, ...)``` both, posts an...

# getting-started

[Marko Novaković]

data class Comment(...)
data class Post(val comments: List<Comment>, ...)

both, posts and comments, are exposed as `Flow`s.
I want a flow that re-emits every time either posts or comments change.
what is the best way to do that?
the approach should be something like this:
1. split Flow<List<Post>> into individual Flow<Post>
2. observeComments(posts.id).flatMapLatest { post.copy(comments = it) }
3. merge `Flow<Post>`s into single Flow<List<Post>>
???

[Mariusz Sołtysiak]

https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/merge.html maybe just merge them but without making single flow?

[Marko Novaković]

I need List<Post> at the end. how can I get that with merge?

[Mariusz Sołtysiak]

Sorry, I misunderstood what you try to achieve

[Rok Oblak]

for combining individual emissions into a collection, you can use fold, or specifically runningFold which will start with an accumulator (empty mutable list) and start adding new emissions to it.

[Marko Novaković]

this worked and it’s passing all the tests:

postsRepository
      .observePosts(feedIds)
      .flatMapLatest { posts ->
          combine(
            flows =
            posts
              .map { post ->
                postsRepository
                  .observePostComments(post.id)
                  .mapLatest { post.copy(comments = it) }
              },
            transform = { it.toList() },
          )
            .onEmpty { emit(persistentListOf()) }
            .mapLatest { it.toImmutableList() }
        )
      }