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kotlinlang

I have `A` class like this:
```data class A(val listOfB: List&lt;B&gt;)```
And `B` is a sealed interface which has multiple children like this:
```sealed interface B
object C: B
object D: B
.....```
Ok, now I have a list of `A`  and each item holds a list of `B`, what I want is to return the `A` list contains *only* the `C` items in each `B` list.
I mean that I want to remove each item that isn't `C` from each `B` list in `A` list

What is the straight forward way to do that?

```val cList = aList.flatMap { it.filterIsInstance&lt;C&gt;() }```

Sorry for the unclear question at first, I updated the question, is it clear now?

```aList.filter { a -&gt; a.listOfB.all { b -&gt; b is C } }```

Doesn't work, This will *not* return the `A` item if wasn't all `B` items type is `C`, but what I want to filter is each `B`  list not the `A` list.

Then you need to use copy or arrow optics probably

```val filteredAList: List&lt;A&gt; = aList.map { a -&gt; a.copy(listOfB = a.listOfB.filterIsInstance&lt;C&gt;()) }```