[REBOL] Re: Series comparison techniques
From: greggirwin:mindspring at: 14-Aug-2003 9:09
Hi Ashley,
AT> search-series: func [series [series!] operator [string!] value] [
AT> clear rowids
AT> switch operator [
AT> "=" [operator: :equal?]
AT> "<>" [operator: :not-equal?]
AT> "<" [operator: :lesser?]
AT> ">" [operator: :greater?]
AT> "<=" [operator: :lesser-or-equal?]
AT> ">=" [operator: :greater-or-equal?]
AT> "like" [operator: :find]
AT> ]
Did you consider passing the operators in directly as the argument, rather
than passing a string and mapping it?
Re: FIND
AT> ...returned results in .015, .063 and .59 seconds respectively. Which got me
AT> thinking about *how* REBOL could do this given:
AT> 1) The series is not sorted
AT> 2) Values are not unique
AT> 3) Runtime increases at a lesser rate than data volume
Natives, like FIND and SELECT, are always preferred for performance
reasons. If you look at the line inside your loop:
if operator series/:pos value [insert tail rowids pos]
You're calling IF on every iteration. Even if it's a native, that's
still a function call with overhead. OPERATOR will also require a
call, so that's two. Then SERIES/:POS has to be evaluated, which means
path evaluation, bounds checking, and lookup. Finally VALUE has to be
evaluated as well. And while REPEAT is pretty efficient, it's not
going to compete with a native machine code loop.
I still find it instructive to test various constructs to see how fast
they are. Sometimes things will surprise you.
-- Gregg
