Hi,
some days ago I faced the time taken by unpack compared to other ways of extracting fields from records.
I think that using substr can speed up the things.
After your posting I took the occasion to learn how to use Benchmark and tested this code below on a 400000-record file:
#/usrl/bin/perl -w

use Benchmark;

$filename = @ARGV[0];

timethese (
   $count,
   {'Method One' => '&One',
    'Method Two' => '&Two',
    'Method Three' => '&Three'}
 );

sub One {
   open(FILE,@ARGV[0]);
   while($row=<FILE>) {
      @data = unpack('a4a2a2a2a2',$row);
   }
   close(FILE);
}
sub Two {
   open(FILE,@ARGV[0]);
   while($row=<FILE>) {
    ($data[0],$data[1],$data[2],$data[3],$data[4]) =
    unpack('a4a2a2a2a2',$row);
   }
   close(FILE);
}

sub Three {
open(FILE,@ARGV[0]);
   while($row=<FILE>) {
    $data[0] = substr($row,0,4);
    $data[1] = substr($row,4,2);
    $data[2] = substr($row,6,2);
    $data[3] = substr($row,8,2);
    $data[4] = substr($row,10,2);
   }
   close(FILE);
}

[download]
and I got this.

Method One: 43 wallclock secs (40.72 usr +  1.23 sys = 41.95 CPU) @  0
+.02/s (n=1)
            (warning: too few iterations for a reliable count)
Method Two: 43 wallclock secs (41.50 usr +  1.42 sys = 42.92 CPU) @  0
+.02/s (n=1)
            (warning: too few iterations for a reliable count)
Method Three: 36 wallclock secs (33.76 usr +  1.42 sys = 35.18 CPU) @ 
+ 0.03/s (n=1)
            (warning: too few iterations for a reliable count)

[download]
Again I think sub Three approach (substr) proves to be faster than sub One (unpack into an array) or Two (unpack into array elements).
Hope this may help.

ciao,
Roberto

In reply to Re: Assining data to an array is slow.. by rbi
in thread Assining data to an array is slow.. by smferris

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