Re: Updating 1 array affects the other array

I've tried changing the name of the array but does'nt work.I just ca'nt understand why updating this array will affect another array of a different name

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]

Make a change to $bar[0][0], and you're also changing $bar[1][0] because they are one and the same. It doesn't matter if you rename @bar to @barbar if you still asing $bar[0] and $bar[1] the same reference.

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

Comment on Re: Updating 1 array affects the other array Download Code

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Re^2: Updating 1 array affects the other array by iphony (Acolyte) on Sep 02, 2008 at 08:21 UTC
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!	[reply] [d/l]
Re^3: Updating 1 array affects the other array by Anonymous Monk on Sep 02, 2008 at 08:42 UTC
...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?	[reply] [d/l] [select]