in reply to RE: RE: List non-matching files
in thread List non-matching files

IMHO, yes. The for version doesn't build a (possibly huge) list of the form ("x",1,"y",1,...) and then populate the hash; it just populates the hash. I suspect my "slice" version is the fastest... and: 

use Benchmark;
@arr=('file.html')x1024;
timethese( -3, {
    'Slice' => '%x=();@x{@arr}=(1)x@arr',
    'For' => '%x=();for(@arr){$x{$_}=1}',
    'Map' => '%x=map{$_=>1}@arr'
} );
__END__
Benchmark: running For, Map, Slice, each for at least 3 CPU seconds...
   For: 3 secs (3.13 usr + 0.00 sys = 3.13 CPU) @ 707.72/s (n=2218)
   Map: 3 secs (3.14 usr + 0.00 sys = 3.14 CPU) @ 96.98/s (n=305)
 Slice: 4 secs (3.14 usr + 0.00 sys = 3.14 CPU) @ 1074.72/s (n=3380)

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...it is (for at least one case). So "slice" is 50% faster than "for" which is much faster than "map" (with tilly's patch, "map" will probably still be slower than the others, but not nearly that slow).

        - tye (but my friends call me "Tye")

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RE: RE: RE: RE: List non-matching files
by fundflow (Chaplain) on Aug 19, 2000 at 00:50 UTC
    Cool, code was updated.

    BTW, i was suspecting that your benchmark was wrong since you used the same value in the hash (file.html). A quick check showed that it doesn't matter much. Interesting.

    This is your code with @arr replaced with @ARGV. The directory has 336 files. (Also, -3 didn't work for me here) 
    >./benchnom *
Benchmark: timing 5000 iterations of For, Map, Slice...
       For: 10 secs ( 9.94 usr  0.00 sys =  9.94 cpu)
       Map: 21 secs (21.26 usr  0.00 sys = 21.26 cpu)
     Slice:  8 secs ( 7.27 usr  0.00 sys =  7.27 cpu)
38.57u 0.05s 0:38.88 99.3%
> ls -l | wc -l
     336
>perl -v

This is perl, version 5.004_04 built for sun4-solaris

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    Similar results were for perl 5.5
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In Section Cool Uses for Perl