looping 2 times through 5000 differs from 5000 times through 2

Hi all,

Last week I discovered this perl.beginners group.
Good stuff here, albeit many times hard to grasp
the answers. But I'm learning.

What I would like to understand is why looping
2 times through 5000 lines takes less time than
looping 5000 times through 2 lines.

To show what I mean, I wrote a snippet that
does nothing with the data and yet the first
part is 5 times faster than the second part
(in my pc anyway).

Thanks.
Rob.


#!/usr/bin/perl

use strict;
use warnings;
use POSIX qw(clock);

#just create a small array for this test
my @few=();
for my $i(1...2){push @few, $i};

#just create a big array for this test
my @many=();
for my $i(1...500000){push @many, $i};

# part 1, loop few times over much data
my $time_1=clock();
foreach my $val (@few){
    foreach my $other(@many) {} #do zilch
}
my $time_2=clock();
my $delta1=$time_2-$time_1;
print "Delta1 $delta1\n";

# part 2, loop many times over few data
my $time_3=clock();
foreach my $val (@many){
    foreach my $other(@few) {} #do zilch
}
my $time_4=clock();
my $delta2=$time_4-$time_3;
print "Delta2 $delta2\n";

exit 0;