Hi just wondering is there an idiomatic iteration ...

# getting-started

[Lucas]

Hi just wondering is there an idiomatic iteration pairwise over a list or array, eg: a b c d iterated as a b; b c; c d. This is to calculate the delta between elements

[diesieben07]

val list = listOf(1, 2, 3, 4, 5, 6)
println(list.zipWithNext())

[diesieben07]

Prints:
[(1, 2), (2, 3), (3, 4), (4, 5), (5, 6)]

[Lucas]

thank you!!! ✌️✌️✌️

[Lucas]

Out of curiosity is there a way to keep mapping functions returning arrays instead of lists? (I'm Assuming there is better performance with arrays because the items should be linearly in memory)

[phldavies]

if you want to transform pairwise, zipWithNext also takes a transformation. i.e.

list.zipWithNext { a, b -> a - b }

[Lucas]

That is beautiful

[phldavies]

if you just want to iterate and process, without mapping to a collection, you can use a sequence

[diesieben07]

Lists use arrays under the hood, there should not be a significant performance difference.

[phldavies]

however you can avoid the intermediate lists when using multiple steps (or just iterating over the result) by using sequences, which may have an impact on performance.

[Lucas]

Nice, so it sounds like Sequence is a generic forward iterator like iter() in python

[karelpeeters]

But then the lambdas aren't inlined so it's a tradeoff unfortunately. And either way everything is going to be boxed, so performance won't be great.

[Lucas]

Yeah I was kind of looking around for a numpy type thing for kotlin...

[Matej Drobnič]

https://youtrack.jetbrains.com/issue/KT-21997 implementing this would eliminate the issue

[Matej Drobnič]

although it doesn't look like a simple problem to solve