What about ```val items = ingredentsList.flatMap {...

# stdlib

[karelpeeters]

What about

val items = ingredentsList.flatMap { listOf(ListItem.HeaderItem(it.type), ListItem.IngredientItem(it)) }

? HeaderItem will need a correctly implemented `equals`/`hascode` for this.

[leosan]

hmm in this case the order of items collection matter actually

[karelpeeters]

That's why I asked ☺️

[leosan]

it has to be

Header
Item
Item
Header
Item
Item 
...

[leosan]

sorry only realized now 😅

[karelpeeters]

You could do this:

val items = listIngredients.groupBy{ it.type }.flatMap {listOf(ListItem.HeaderItem(it.key)) + it.value.map { ListItem.IngredientItem(it) } }

but that starts to get forced.

[leosan]

what you mean by forced?

[karelpeeters]

It's less readable then the original, and you're creating a bunch of useless lists along the way.

[leosan]

oh I see

[leosan]

I was looking at koans collections examples, but I couldn't find anything close to what I want, maybe fold but I'm not sure how to use it

[ilya.gorbunov]

@karelpeeters Your proposal with flatMap is fine, just format it nicely and it would be as readable as the original with ArrayList.