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;
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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!