Question

Here is where I begin. I am reading arrays from a database one at a time using a while loop. I want to pick up on elements from the database that are duplicates (on certain fields). I want to keep only the items that are unique on these fields. Then I want to print out the data I have kept in a certain way. I created the code I thought would do it, but it gives me everything including items which are duplicates on the field. I’ve been searching and searching and I can’t figure it out, I’m thinking, as a perl noob, I am missing something simple. Code is as follows:

my @uniques = ();
my $output;

while (my @itemArray = $sth->fetchrow_array() ) {
    my $duplicateFlag = 0;  
    foreach (@uniques){
        if(  ($itemArray[3] eq "$_->[3]") and ($itemArray[4] eq "$_->[4]")
               and ($itemArray[5] eq "$_->[5]" ) and ($itemArray[6] eq "$_->[6]" )
               and ($itemArray[7] eq "$_->[7]" ) and ($itemArray[8] == "$_->[8]" ) ){
            $duplicateFlag = 1;
        }
    }
    if( $duplicateflag == 0){
        $refToAdd = \@itemArray;
        push(@uniques, $refToAdd);
        $output .= "$itemArray[3]" . "\t$itemArray[8]" . "\t$itemArray[5]" . "\t$itemArray[7]\n";
    }
}
print $output

Answer 1

You are getting all the duplicates because $duplicateflag is undefined at line 13. Running a syntax test on your script with use strict; use warnings; on produces the following warning:

Global symbol "$duplicateflag" requires explicit package name at t10.pl line 18.

And if we scrutinize your definition of “that” variable, it says:

my $duplicateFlag = 0;

Which is to say, you have a capital F, which means $duplicateflag is not the same variable as $duplicateFlag. The check undef == 0 still produces a true value and causes a false positive.

To avoid problems like this, always run your scripts with

use strict;
use warnings;