what is the ideomatic way to get a copy of an Arra...

# getting-started

[frogger]

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

[Egor Okhterov]

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

[frogger]

I don't think so @Egor Okhterov:

Returns a list containing all elements except last n elements.

[Egor Okhterov]

array.dropLast(n)

[frogger]

n as in any index, not necessesarily the last one

[Egor Okhterov]

n is the number of elements

[Shawn]

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

[Shawn]

you can do this:

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

[Shawn]

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

[frogger]

n is the number of elements

bold claim

[Egor Okhterov]

Oh, you mean without n'th element

[Egor Okhterov]

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

[frogger]

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

[diesieben07]

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

[Shawn]

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]

That's 3 array copy operations

[Shawn]

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

[diesieben07]

And it's allocating 3 new arrays

[Shawn]

just iterating on my last suggestion

[frogger]

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

[Egor Okhterov]

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

[tseisel]

If you are using arrays instead of lists for performance reasons, you should stick with System.arraycopy (JVM-only).

[diesieben07]

(Which is what copyInto uses)