On Thu, Aug 26, 2010 at 11:53 AM, Chouser <chou...@gmail.com> wrote: > 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).
I messed up the analysis of the complexity there. It may actually be worse than O(n), and there may be a more efficient solution. --Chouser http://joyofclojure.com/ -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
