in reply to
Assining data to an array is slow..
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);
}
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)
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
