On Mon, Aug 17, 2009 at 11:35 PM, Mark Triggs <mark.h.tri...@gmail.com>wrote:
> > Thanks all. So combining a few suggested ideas: > > (defn slice > "Return the items in coll at index positions keys. > > (slice [0 4 6] \"abcdefg\") => (\\a \\e \\g)" > [keys coll] > (let [max-idx (apply max keys) > keyset (set keys)] > (map second > (filter (fn [[idx _]] (keyset idx)) > (take-while (fn [[idx _]] (<= idx max-idx)) > (indexed coll)))))) > > This version has the advantage of working on infinite sequences and not > hanging onto the head. This works as expected: > > (slice [200 201] (repeatedly #(int-array 102400))) > > without blowing up the stack or throwing OutOfMemory (on my JVM). So does the very simple (defn slice [indices coll] (map #(nth coll %) indices)) though that doesn't use keys rather than position with maps. (defn slice [indices coll] (map #(get coll %) indices)) does, but works for maps and vectors but not lists. It does work for strings. (defn slice [indices coll] (map #(get (indexed coll) %) indices)) should if (indexed coll) has the semantics it seems it should from what you've posted, but the indexed function is apparently bleeding-edge because my copy of clojure 1.0 doesn't have anything by that name in it. (defn slice [coll & indices] (map #(nth coll %) indices)) has the same argument syntax as suggested originally by Mark. --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
