I have a list of valid ids in a complex class (in my example a Pair). I have a separate list of ids...

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[Paul N]

I have a list of valid ids in a complex class (in my example a Pair).

I have a separate list of ids.

What's the best way of filtering the lists of ids to only contain ids that are present in the first case ? I'm using map to convert the list of pairs to a list of ids and then using contains in the example below. Is there a better way ?

@Test
    fun `test filter`() {

        val cars = listOf("1" to "Jag","2" to "Mini")

        val ids = listOf("1","2","3")

        val validIds = ids.filter { cars.map { it.first }.contains(it) }

        validIds `should equal` listOf("1","2")

    }

[Bornyls Deen]

You could use any to avoid having to create a new list of car ids with every iteration

ids.filter { id -> cars.any { it.first == id } }

[Paul N]

thanks, I haven't used any before, will look that up.

[araqnid]

if the list of cars was big, pulling out the keys/first values into a Set might be worthwhile

[Bornyls Deen]

I was thinking the same but wasn't 100% sure on the performance benefits.

something like this maybe

val cars = listOf("1" to "Jag", "2" to "Mini")
val carIds = cars
    .map { car -> car.first }
    .toSet()

val ids = listOf("1", "2", "3")
val validIds = ids.filter { id -> carIds.contains(id) }