----- Original Message -----
From: "JupiterHost.Net" <[EMAIL PROTECTED]>
Date: Tuesday, January 25, 2005 11:01 am
Subject: Re: hash slice/exists vs. grep benchmark weirdness...
> > You have to stop spending so much time playing with all this bogus
> > benchmarking :)
>
> It not bogus :) Its an example to find the best method for a project.
>
> If you prefer I'll ask the question I was trying to answer with
> the
> benchmark:
>
> Assuming you have an array of 0-15 elements is it quicker/more
> efficient to:
>
> 1) create a hash slice and use exists when checking for specific
> onesor
> 2) grep a regex out of the array when checking for specific ones
>
> >>slice:
> >>use strict;
> >>use warnings;
> >>my @k=qw(1 2 3 4 5 6);
> >>my %n;@[EMAIL PROTECTED] = @k;
> >>print "hi" if exists $n{1};
> >>print "hi" if exists $n{3};
> >>print "hi" if exists $n{5};
> >>print "hi" if exists $n{7};
> >>print "hi" if exists $n{9};
> >>print "hi" if exists $n{11};
> >>
> >>grep:
> >>use strict;
> >>use warnings;
> >>my @k=qw(1 2 3 4 5 6);
> >>print "hi" if grep /^1$/, @k;
> >>print "hi" if grep /^3$/, @k;
> >>print "hi" if grep /^5$/, @k;
> >>print "hi" if grep /^7$/, @k;
> >>print "hi" if grep /^9$/, @k;
> >>print "hi" if grep /^11$/, @k;
> >>
> >>Benchmark: timing 5000000 iterations of grep, slice...
> >> grep: 3.65945 wallclock secs ( 2.33 usr + 0.04 sys =
> 2.37 CPU)
> >>@ 2109704.64/s (n=5000000)
> >> slice: 2.37966 wallclock secs ( 2.52 usr + -0.01 sys =
> 2.51 CPU)
> >>@ 1992031.87/s (n=5000000)
> >> Rate slice grep
> >>slice 1992032/s -- -6%
> >>grep 2109705/s 6% --
> >>
> >>I would've thought the "slice and then use exists" would have
> been
> >>faster then "greping the entire array each time and using
> regexes" when
> >>you check it. but its consistently faster by an average 6-10%
> >>
> >>Any ideas why that might be?
> >
> > Well, first -- you're creating the hash inside the benchmark loop,
> > which is not particularly light-weight.
>
> Good point,
> although in the real world app I'll have an array already so I
> want to
> see if its quicker to:
> - make the hash via a slice and use exists
> or
> - just grep the whole array each time with a regex
> If I use
> my %hash = qw(1..20000);
> and exists
> vs.
> my @array = qw(1..10000);
> IE - no slice
>
> then exists is a bit faster 2% or so, the problem is I start with
> an
> array I have no control over.
>
> So, I'd have to do a slice to get the hash (or loop through it or
> otherwise do something to get the hash)
>
> > Second: You're using pathologically small lists. Try running
> it with
> > 10,000 elements instead of ten.
>
> that makes them about even, with slice being 1% faster at times,
> however
> the size of the array in the real world app are similar to the
> original
> benchmark
>
> > Third: Premature optimization is a terrible thing.
>
> Premature? Could you elaborate?
Just as an FYI, you don't need "exists" in your code at all. It is just a waste
of time in your example. Should be beter writen as:
print "hi" if $n{11};
>
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>
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