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kotlinlang

Is there a way to flatten the amount of calls to flatMap?

```myScreenState.listOf20Items.flatMap { it.subListOf10Items }.flatMap { it.anotherSubListOf10Items }
        .filter { it.isDone }.size```
i was initially thinking maybe I could do

```myScreenState.listOf20Items.flatMap { it.subListOf10Items.anotherSubListOf10Items }
        .filter { it.isDone }.size```


are you concerned about the performance impact of chaining the flatMaps? Personally I wouldn’t worry about it, because it’s usually not going to be _that_ bad.

If you wanted to avoid problems with chained flatMaps it you could use a <https://kotlinlang.org/docs/sequences.html|Sequence>. This can help with performance, but it can also hinder it

There’s also `count {}`, which you can use instead of `filter {}.size`

I think this is nice and readable:

```myScreenState
  .listOf20Items
  .asSequence()
  .flatMap { it.subListOf10Items }
  .flatMap { it.anotherSubListOf10Items }
  .count { it.isDone }```


not concerned about perf. just that two flat maps in a row seems "weird" and didn't know if there was a shorthand to chained flatmaps.