so I have a list of orders and then a list of cars...

# getting-started

[oday]

so I have a list of orders and then a list of cars, when I get the list of cars I would like to take from it all the cars whose id exists in the list of orders

[oday]

isn’t it cars.filter { it.id in orders } ?

[diesieben07]

If orders is a list of car IDs - yes.

[oday]

it is a list of objects, each has a carId

[oday]

yea I thought I needed like iterator() or another find or something?

[oday]

its basically a double for loop

[Martin Cazares]

you could flush the order.ids into a hashset to make it faster...

[diesieben07]

cars.filter { car -> orders.any { order -> order.carId == car.id } }
Or as Martin says, first make a set of car ids from all orders, if this is performance critical code.

[oday]

Ahh, any

thank you that does it

[oday]

back to my example

[oday]

if I wanted to then say car.order = order

[oday]

chaining a .map after the filter doesn’t grant me the order, i just get the car of course

[oday]

i can do it after the .any Ithink

[oday]

nah I can’t, especially if order is val, I need to return the desired cars as car.copy(order = neworder) later

[oday]

for (result in listings.results) {
    for (order in orders) {
        if (result.id == order.listingId) {
            purchasedCars.add(
                result.copy(
                    order = order,
                    contactOptions = emptyList(),
                    isFavorite = true
                )
            )
        }
    }
}

[oday]

this is what I’d like to do

[oday]

to also act on the cars I found according to the any , in the same chain

[diesieben07]

listings.results.flatMapTo(purchasedCars) { result ->
    orders.mapNotNull { order -> 
        if (result.id == order.listingId) {
            result.copy(...)
        } else null
    }
}

or something like that

[diesieben07]

But you should really use a map indexed by ID here so that you don't have to loop through the lists all the time