Kotlin - Functionally Traverse Collection getting current/next value

user_497753 0
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In Kotlin, is there a functional way to traverse through a List<T> getting a Pair<T,T> that reflect the current/next element.

E.g. - the imperative approach would be something like 

for (index in 0 until list.size-1) {
        val current = list[index]
        val next = list[index + 1]
        //do calculations on current/next.
    }

Something like list.forEachPaired { it: Pair<String,String?> ->//do something }

kotlin
3 Answers

windowed (see link for the parameters). If you want to work with Pairs in particular, you can use the overload with transform:

list.windowed(2) { Pair(it[0], it[1]) }.forEach { ... }

but I'd just write 

list.windowed(2).forEach { ... }

where the parameter of forEach's lambda is a List<T> of length 2.

alexey_r_92040

Although windowed() is powerful, there's a slightly simpler alternative in this case: zipWithNext(). For example:

list.zipWithNext().forEach{ (first, second) ->
    // ...
}
user_101342090

I agree with Alexey Romanov that the intermediate Pairs are not necessary really. You can destructure your windowed lists in a forEach lambda:

list.windowed(2).forEach { (first, second) ->

}
user_80736520
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