I want to find an item in a list When I find it I also want kotlinlang #getting-started

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Title

Colton Idle

01/21/2022, 6:29 AM

I want to find an item in a list. When I find it, I also want the index of it. I have found

list.indexOfFirst

and

list.first

but is there some way to get both?

ephemient

01/21/2022, 6:35 AM

list.withIndex().first { predicate(it.value) }

👀 1

Albert Chang

01/21/2022, 6:58 AM

If your list is a random access list (such as

ArrayList

), getting the index and then retrieving the value using the index is more efficient as the access is O(1) and there’s no additional object allocations which isn’t the case when using

withIndex()

👍 1

ephemient

01/21/2022, 7:12 AM

this is true, and almost every list you will commonly encounter except

LinkedList

RandomAccess

Colton Idle

01/21/2022, 7:30 AM

So theres basically no way to do it in one call (what Albert is recc'ing)? Basically just find the index first, then grab the item with said index. No fancy idiomatic kotlin function or something available?

ephemient

01/21/2022, 7:39 AM

you could put a nice wrapper around

val (index, value) = run {
    list.forEachIndexed { index, value ->
        if (predicate(value)) return@run IndexedValue(index, value)
    }
    throw NoSuchElementException()
}

or something, but otherwise, pick fast (indexOf) or concise (withIndex)

Colton Idle

01/21/2022, 7:45 AM

fast it is! Glad I wasn't missing any cool function I just didn't stumble upon, but I did TIL

withIndex

Thanks as always @ephemient and @Albert Chang

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