Is there a collection function to pair one element with all others from the same list? For example: ...

# codereview

[delblanco]

Is there a collection function to pair one element with all others from the same list?
For example: given listOf(A,B,C) I would like to end up with the following pairs: A to B, A to C, B to C
Currently I got something like this but it feels non-idiomatic and inefficient...

val users = listOf(User("A"), User("B"), User("C"))
	val chats = users.flatMap{ u1 ->
        users.filterNot { u1 == it }
            .map { u2 -> Chat(setOf(u1, u2)) }
    }.toSet() // filters out duplicates

[bjonnh]

Does the order matter?

[bjonnh]

Instinctively I would have done:

val l = listOf("A", "B", "C", "D")
 l.flatMapIndexed { i, a ->
    l.subList(i+1, l.size).map { setOf(a,it) }
}

[bjonnh]

If your lists are not too big that should be fine to go over them like that many times

[delblanco]

Totally forgot to reply
No, order doesn't matter and the list is not that big.
I like your solution more as it doesn't require filterNot nor the toSet to filter duplicates
thanks!