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push @{ $data{ $cols[ 0 ] } }, pack 'C*', @cols[ 1 .. $#cols ];

 my $mask = $keyset1 ^ $keyset2;
                next unless 1+ index $mask, chr( 0 );
...
                print join ', ', map{
                    substr( $mask, $_, 1 ) eq chr(0)  ? $_+1 : ()
                } 0 .. length( $mask )-1;