On Mon, Sep 26, 2011 at 9:12 AM, Paul Richards <paul.richa...@gmail.com> wrote: > Hi, > How can I efficiently pick a random element from a sorted-set? > > If I try rand-nth I get this: > user=> (rand-nth (sorted-set 1 2 3)) > java.lang.UnsupportedOperationException: nth not supported on this > type: PersistentTreeSet (NO_SOURCE_FILE:0) > > I can get this expression to work if I naively apply seq: > user=> (rand-nth (seq (sorted-set 1 2 3))) > 1 > > However this performs very badly on large sets. Is there a more > efficient way to do this? > > (I need to keep my elements in a sorted-set for other parts of the > application, where I rely on subseq.)
Try just getting the value with rand-int directly. The sorted-set uses a tree map underneath, so look up time is consistent with a map. Also, count is O(1). (get foo (rand-int (count foo))) -- 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
