On Thu, Aug 26, 2010 at 9:44 AM, Jon Seltzer <seltzer1...@gmail.com> wrote:
> I know what assoc does:
>
> user=> (assoc [\a \b \c] 0 \d) ;please extend to much larger vector
> with index somewhere in the middle
> [\d \b \c]
>
> but what if I want:
>
> user=> (assoc-x [\a \b \c] 0 \d) ;is there an assoc-x
> [\a \d \b \c]
>
> I don't see a function that does this. I'm sure I'm missing it. I,
> of course, know this could be done with a combination of other
> functions like subvec and/or into but it seems fundamental enough to
> have its function.
The internal structure of vectors is such that this cannot be
done efficiently, which is why no function to do it is included
in clojure.core. You can do it inefficiently like this:
(let [v '[a b c d e f]
i 3]
(into (subvec v 0 i) (cons 'X (subvec v i))))
;=> [a b c X d e f]
That's about as good as you're going to get with vectors, O(n)
where n is (- (count v) i).
--Chouser
http://joyofclojure.com/
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