The IRC channel folks helped me implement what we discovered was
already called "separate" in contribs. My point was to do a partition
that generated the two lists "(passes pred)" and "(fails pred)" in one
pass without recursion.
We ended up with:
(defn filt-rem [pred coll]
(loop [l1 () l2 () [f & r] coll]
(if f
(if (pred f)
(recur (conj l1 f) l2 r)
(recur l1 (conj l2 f) r))
(list l1 l2))))
-- the name reaming "filter and remove", I was thinking
There's some branching there, so perhaps it's not the most efficient
code.
Here's what's in contrib, and as Tim showed me in the pquicksort
discussion, that last bit could be replaced by "remove":
(defn separate
"Returns a vector:
[ (filter f s), (filter (complement f) s) ]"
[f s]
[(filter f s) (filter (complement f) s)])
Well, the recursive one that does two passes blows away filt-rem,
according to 'time'. But if I just count in my head, they both take
about as long.
Yes, I started throwing doall all over the place. The other thing is
we definately aren't talking about milliseconds. I.m not trying to
measure how much time is spent in the reader or compiler or whatever.
I care about the user waiting for the answer, and that's what I'm
trying to time.
Here's what I'm seeing, even though I don't believe it:
(def l1 (doall (take 50000 (repeatedly #(rand-int 3000))))) ;;; I
don't know if doall goes there, just shotgunning it at this point
(time (filt-rem #(< % 1500) (doall l1))) ;;;; I've tried doall in
various places with no help
"Elapsed time: 63.158 msecs" <------ no way. It took like 12
seconds
(time (separate #(< % 1500) (doall l1))) ;;;;;; doall here
actually did something even though already done above
"Elapsed time: 12.701 msecs" <----------- no way. 12 seconds, I
counted. Definitely longer than 12 msecs.
Questions:
1) Is there anything wrong with filt-rem or anything to improve it?
2) why are the times reportedly so different when I can tell they
return in about the same amount of time?
Thanks.
--~--~---------~--~----~------------~-------~--~----~
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
-~----------~----~----~----~------~----~------~--~---
