How can I remove duplicated consecutive values in ...

# advent-of-code

[Mikael Alfredsson]

How can I remove duplicated consecutive values in a list by a specific field? [{a,1},{b,1},{c,2},{d,2},{e,1}] -> [{a,1}{c,2},{e,1}]

[ephemient]

https://kotlinlang.slack.com/archives/C0922A726/p1629199729456400

[ephemient]

although if that is exactly your use case, something simple like

var previousValue: Int? = null
list.filter { (key, value) ->
    value != previousValue.also { previousValue = value }
}

will work, even if it's "cheating" a bit by using mutable state outside the lambda

[Mikael Alfredsson]

hum, nothing with reduce or fold that (even if it under the hood might do the same) looks cleaner?

[Fredrik Rødland]

don't know about the "looks cleaner" part, but:

listOf('a' to 1, 'b' to 1, 'c' to 2, 'd' to 2, 'e' to 1)
            .fold(emptyList<Pair<Char, Int>>()) { acc, el ->
                if (el.second != acc.lastOrNull()?.second) {
                    acc + el
                } else {
                    acc
                }
            }

[Paul Woitaschek]

I’d go for windowed:
https://gist.github.com/PaulWoitaschek/46877e4f17b32c112ad2ccde06d93d9b

[Mikael Alfredsson]

Thanks for all the solutions. Never used windowed, so something new to learn.