Is there `OrderedSet` (not sorted) in Kotlin? Any alternatives?

# getting-started

[Priya]

Is there OrderedSet (not sorted) in Kotlin? Any alternatives?

[ephemient]

the built-in setOf(), mutableSetOf(), mapOf(), mutableMapOf(), and returns of most methods such as .toSet(), .toMap(), etc. are documented to preserve insertion order

[Priya]

How can I get or takeLast(N) the last N items in a set without using reversed().take(N) ? Sets doesn’t seem to support takeLast

[ephemient]

iteration order is defined but they are not indexable nor do they provide a reverse iterator, so there is no efficient way to takeLast

[Priya]

Any suggestions on an efficient way to 1) have unique values 2) and retrieve last n items?
My current solution:
mutableSetOf(1,2,3,1).reversed().take(3).reversed()

[ephemient]

the most concise you could do is .toList().takeLast(N)

[ephemient]

but if this is your only goal I think you'd be better off with a different data structure

[Priya]

Any suggestions for a diff data structure that can handle this scenarios?

[ephemient]

val lastN = ArrayDeque<T>(N)
for (item in items) {
    if (lastN.size == n) lastN.removeFirst()
    lastN.addLast(item)
}

[Priya]

Thanks! appreciate the quick response 👍

[Paul Griffith]

Will be a long time before it makes it way into Java (and thus, Kotlin) but this JEP would extend Java collections to allow this: https://openjdk.java.net/jeps/8280836