On Thu, Feb 26, 2009 at 12:02 PM, Jason Wolfe <jawo...@berkeley.edu> wrote: > > Hi Mark, > > The results will depend on the objects you are comparing. If you need > to search through the list multiple times, converting to a set once is > almost certainly going to be faster. But, if you're just doing it > once, iterating will usually be much faster:
That makes sense, but doesn't match the results I see. See my additional detail below. > user> (time (dotimes [_ 100000] (contains? (set (range 100)) 10))) > "Elapsed time: 7708.336 msecs" > > user> (time (dotimes [_ 100000] (some #(= 10 %) (range 100)))) > "Elapsed time: 291.474 msecs" > > user> (time (let [s (set (range 100))] (dotimes [_ 100000] (contains? > s 10)))) > "Elapsed time: 27.978 msecs" > > In a simple test I get similar results for strings too... what > conditions were you testing under? Here's the actual code I ran to test. (def stooges (list "0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "Moe" "Larry" "Curly")) (time (dotimes [_ 1000] (some #(= % "Curly") stooges))) (time (dotimes [_ 1000] (contains? (set stooges) "Curly"))) (let [s (set stooges)] (time (dotimes [_ 1000] (contains? s "Curly")))) I'm seeing a wide variation in results. Here are results from consecutive runs. "Elapsed time: 40.515 msecs" "Elapsed time: 121.825 msecs" "Elapsed time: 1.163 msecs" "Elapsed time: 69.026 msecs" "Elapsed time: 60.438 msecs" "Elapsed time: 1.732 msecs" So sometimes converting to a set for a single lookup (the second case) is faster, but not usually. > On Feb 26, 7:53 am, Mark Volkmann <r.mark.volkm...@gmail.com> wrote: >> I thought for sure it would be faster to use "some" to determine >> whether an item was in a list rather than convert the list to a set >> and then use "contains?", but it turns out I was wrong. The latter >> approach takes about 1/3 to 1/2 the time! This is the case even when >> the list contains 100 items. Of course I realize that if this is a >> commonly needed operation for a particular collection, it's better to >> use a set instead of a list in the first place. >> >> (def stooges (list "Moe" "Larry" "Curly")) >> (time (some #(= % "Curly") stooges)) >> (time (contains? (set stooges) "Curly")) -- R. Mark Volkmann Object Computing, Inc. --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
