what is the ideomatic way to get a copy of an Array without kotlinlang #getting-started

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Title

frogger

01/21/2020, 10:12 AM

what is the ideomatic way to get a copy of an Array without element

Egor Okhterov

01/21/2020, 10:17 AM

val array = arrayOf(1, 2, 3)
val slice = array.dropLast(1)

frogger

01/21/2020, 10:23 AM

I don't think so @Egor Okhterov:

Returns a list containing all elements except last n elements.

Egor Okhterov

01/21/2020, 10:24 AM

array.dropLast(n)

frogger

01/21/2020, 10:24 AM

as in any index, not necessesarily the last one

Egor Okhterov

01/21/2020, 10:24 AM

n is the number of elements

Shawn

01/21/2020, 10:24 AM

This isn’t a great operation for a Kotlin array - elements aren’t linked so repeated scanning will have to occur to get your result

you can do this:

inline fun <reified T> Array<T>.withoutIndex(index: Int): Array<T> =
    (dropLast(index + 1) + drop(index + 1)).toTypedArray()

but if you need to arbitrarily drop elements within this collection a lot, consider a LinkedList instead?

frogger

01/21/2020, 10:25 AM

n is the number of elements

bold claim

😂 3

Egor Okhterov

01/21/2020, 10:25 AM

Oh, you mean without

n'th

element

👍 2

Usually people use the other variable for that, so I was confused 😃

frogger

01/21/2020, 10:26 AM

No worries, I noticed my question wasn't crystal clear

diesieben07

01/21/2020, 10:29 AM

An optimized version: https://pl.kotl.in/90_QAXN2D

👏 1

Shawn

01/21/2020, 10:30 AM

this might be a hair better?

inline fun <reified T> Array<T>.withoutIndex(index: Int): Array<T> =
    sliceArray(0 until index) + sliceArray((index + 1) until size)

diesieben07

01/21/2020, 10:30 AM

That's 3 array copy operations

Shawn

01/21/2020, 10:30 AM

sorry, didn’t mean relative to your suggestion @diesieben07

just iterating on my last suggestion

diesieben07

01/21/2020, 10:30 AM

And it's allocating 3 new arrays

frogger

01/21/2020, 10:32 AM

Thanks @diesieben07 and @Shawn super helpful, I'll try your suggestions. 📗

👍 1

Egor Okhterov

01/21/2020, 10:33 AM

arr.filterIndexed { i, _ -> i != n }

👍 2

➕ 2

tseisel

01/21/2020, 10:40 AM

If you are using arrays instead of lists for performance reasons, you should stick with

System.arraycopy

(JVM-only).

diesieben07

01/21/2020, 10:40 AM

(Which is what

copyInto

uses)

👍 1

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