Is there a flow operator which allows me to to take the last two events and map them? or do I need t...

# flow

[enighma]

Is there a flow operator which allows me to to take the last two events and map them? or do I need to use a SharedFlow/StateFlow for that?

[wasyl]

You can use a top-level combine for that, or flowA.combine(flowB) { }

[enighma]

But I only have one flow here. So there is no flowA or B only A.

[wasyl]

ah, the last two events of the same flow 🤔 combine(flowA, flowA.drop(1))? Although it would seem useful to have a shared flow to not trigger the collection twice

[enighma]

If it was a regular list I think fold/reduce would make sense.

[enighma]

So whenever FlowA is updated I want to fold the last two values.

[enighma]

A shared flow with a buffer of 2 ought to work, but ideally a regular flow would work

[wasyl]

Yeah I wanted to suggest looking into fold/reduce too. I found something like this in our codebase too:

fun <T> Flow<T>.zipWithPreviousOrNull() = flow {
    var prev: T? = null
    collect { value ->
        emit(prev to value)
        prev = value
    }
}

but I can’t say if it’s the best solution

[enighma]

Yeah, I was thinking about writing my own. It just feels like there should be an operator for this already hehe

[ephemient]

https://github.com/Kotlin/kotlinx.coroutines/issues/1767 there is not a pre-existing operator

[enighma]

Thanks for all the help! It answers my all my questions 🙂

[Stylianos Gakis]

Similarly to the code snippet above, we’ve been using this in our code base https://github.com/HedvigInsurance/android/blob/e2b5df0684487465922a57305abcc2efc0[…]/main/java/com/hedvig/app/util/coroutines/HistoryOfLastValue.kt and it’s been working perfectly fine 😄