Hmm, on the same (micro admittedly) benchmark as above... (time (let [[a b] (unzip-with even? (range 100000))] [(nth a 49999) (nth b 49999)])) "Elapsed time: 177.797 msecs" [99998 99999]
that's a bit slower than both the previous versions. The reduce version does only apply the pred once per item I think? On Sun, Mar 8, 2009 at 12:37 PM, Christophe Grand <christo...@cgrand.net> wrote: > > The question showed up the other day on #clojure with the additional > constraint to evaluate pred only once per item, here is Rich's solution: > > http://paste.lisp.org/display/76458#1 > > (defn unzip-with [pred coll] > (let [pvs (map #(vector (pred %) %) coll)] > [(for [[p v] pvs :when p] v) > (for [[p v] pvs :when (not p)] v)])) > > > Christophe > > David Sletten a écrit : >> I'm reading the Sequences chapter of Programming Clojure, and Stu >> points out that split-with combines the semantics of take-while and >> drop-while. But is there a function that does something similar with >> "filter"? Namely, rather than simply filtering the elements of a >> collection that satisfy a predicate I also want to capture those that >> don't. Something like this: >> (defn filter-split [pred coll] >> (loop [trues '() falses '() coll coll] >> (cond (empty? coll) >> (vector (reverse trues) (reverse falses)) >> (pred (first coll)) >> (recur (cons (first coll) trues) falses (rest coll)) >> :else >> (recur trues (cons (first coll) falses) (rest coll))))) >> >> (filter-split #{\a\e\i\o\u} "is this not pung?") => [(\i \i \o \u) >> (\s \space \t \h \s \space \n \t \space \p \n \g \?)] >> (filter-split even? (range 10)) => [(0 2 4 6 8) (1 3 5 7 9)] >> >> Aloha, >> David Sletten >> >> > >> >> > > > -- > Professional: http://cgrand.net/ (fr) > On Clojure: http://clj-me.blogspot.com/ (en) > > > > > > --~--~---------~--~----~------------~-------~--~----~ 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 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 -~----------~----~----~----~------~----~------~--~---
