Kotlin filter lambda array using iteration index

Question

I would like to filter an array into an array of every nth item. For examples:

fun getNth(array: Array<Any>, n: Int): Array<Any> {
    val newList = ArrayList<Any>()
    for  (i in 0..array.size) {
        if (i % n == 0) {
            newList.add(array[i])
        }
    }
    return newList.toArray()
}

Is there an idiomatic way to do this using for example Kotlin's .filter() and without A) provisioning a new ArrayList and B) manually iterating with a for/in loop?

Just a comment, the code above is just Java masked in a Kotlin file, my recommendation is to you try to look Kotlin code in a different way, this will help you to use everything that we have available. — Tiarê Balbi
– Tiarê Balbi, Commented Oct 21, 2017 at 19:55

Ilya · Accepted Answer · 2017-10-21 23:22:53Z

36

filterIndexed function is suited exactly for this case:

array.filterIndexed { index, value -> index % n == 0 }

answered Oct 21, 2017 at 23:22

Ilya

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Nate Vaughan · Accepted Answer · 2017-10-21 21:04:39Z

13

Use Array.withIndex():

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/with-index.html:

array.withIndex().filter { (i, value) -> i % n == 0 }.map { (i, value) -> value }

edited Oct 21, 2017 at 21:04

Nate Vaughan

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answered Oct 21, 2017 at 19:52

Alexey Romanov

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