$array2[$n] = $array1[$n];
[download]

for my $i (0..$#array1) {
    for my $j (0..$#array2) {
        # do something
    }
}
[download]

...a "cell" in an array of array. e.g. @unique_manufacturer_model->[$i][12]++

A couple of points. The @ should be $ (think singlular, scalar, $) and you don't need the arrow (you have an array and the arrow is trying to dereference a reference to an array). If you had strict and warnings enabled Perl would have complained about it.

It would be well worth straightening out these snags first. Perl will help you if you turn on strict and warnings. :-)

update: fixed typo

Because a name don't mean much when you're modifying references. Example

my @foo = 1 .. 4;
my @bar;
my $someReference = \@foo;
$bar[0] = $someReference;
$bar[1] = \@foo;
$bar[2] = $foo[2];

use Data::Dumper;

print Dumper( \@bar ),"\n";

$bar[0][0]='change';
$bar[2] .= ' foo ';

print " bar[0][0] ", $bar[0][0], "\n";
print " bar[1][0] ", $bar[1][0], "\n";

print Dumper( \@bar ),"\n";

__END__

$VAR1 = [
          [
            1,
            2,
            3,
            4
          ],
          $VAR1->[0],
          3
        ];

 bar[0][0] change
 bar[1][0] change
$VAR1 = [
          [
            'change',
            2,
            3,
            4
          ],
          $VAR1->[0],
          '3 foo '
        ];
[download]

See perldata,perlref,perldsc... and perlmonks own Tutorials

Hi everyone. Thanks for the pointers. I clean up things like removing the arrows. So far it has not work, because there's this part of the code, where I suspect is wrong, but I'm not skilled enough to think of an alternative.

my %seen_values;
my @unique_terminal_id = grep { !($seen_values{$_->[4]}++) } @temp_ope
+n_single;
my %seen_values;
my @unique_manufacturer_model = grep { !($seen_values{$_->[9]}{$_->[10
+]}++) } @unique_terminal_id;
my %seen_values;
my @unique_manufacturer_model_version = grep { !($seen_values{$_->[9]}
+{$_->[10]}{$_->[11]}++) } @unique_terminal_id;
[download]

This portion of code is where I have declared the arrays and just before I encounter the problem. Basically, what I am trying to do is grep unique column pair in a table(array of array) and store them into a new table. I managed to get what I wanted (e.g. the unique pairs), but I ca'nt quite see how it ended up cross-referencing to another array. Thanks!

...but I ca'nt quite see how it ended up cross-referencing to another array.
Let me repeat, it is because you are storing references. If you want copies, use Storable qw(dclone); Observe

my $ref = [ 1,2];
my $another = [3,4];
my @foo = ( $ref, $another);
my @bar = $foo[1];

die $bar[0][1];
__END__
4 at - line 6.
[download]

get it?

@array1=(
    [1,2,3],
    [4,5,6],
    [7,8,9]
);
[download]

$array2[1]=$array1[1]
[download]

$array1[1][0]='something';
[download]

print $array2[1][0]; # shows 'something'
[download]

Hi, thanks for the explanation. I understand your explanation, but I've checked thru my codes but ca'nt see such mistake being committed. The only (write) operations I've done to the arrays (prior to discovering the problem) is shown below. What I am trying to do is to remove duplicate entries (based on certain column combinations) and store them in a new array (those with the "unique" prefix). The "cross-referencing" seems to have been committed here.

my %seen_values;
my @unique_terminal_id = grep { !($seen_values{$_->[4]}++) } @temp_ope
+n_single;
my %seen_values;
my @unique_manufacturer_model = grep { !($seen_values{$_->[9]}{$_->[10
+]}++) } @unique_terminal_id;
my %seen_values;
my @unique_manufacturer_model_version = grep { !($seen_values{$_->[9]}
+{$_->[10]}{$_->[11]}++) } @unique_terminal_id;
[download]

As other people have mentioned, what you're copying are references (as indicated by the de-referencing arrows that you're using in the greps). Namely, your array @temp_open_single is, presumably, an array of arrayrefs.

Let's say that the first arrayref is pointing to the array at 0x18045c0, and that that array passes the test in the grep for @unique_terminal_id. Then @unique_terminal_id also contains a reference to the array at 0x18045c0. Let's suppose further that that array also passes the test in the grep for @unique_manufacturer_model. Then @unique_manufacturer_model also contains a reference to the—exact same!—array at 0x18045c0. It is copying the reference, not the referent.

That means that, when you refer to $unique_terminal_id[0][0] or to $unique_manufacturer_model[0][0], in either case you're just looking at the entry at index 0 of the single array at 0x18045c0. After you change that single array in one place, the changes will still be visible even if you look at it from another location. As others have mentioned, you need something like Storable's dclone function (which makes a 'deep clone') will allow you to avoid this difficulty.