I'm populating, for display, an AoA with a unordered list of serial numbers. I need to group by prefix putting the last read group at the top of the list. The 'X' indicates the prefix read. "num" in the first column is there to display mysteriously added elements.

Display based on __DATA__
     SNO   A  B  C  D
num: 1011  X  X  X  X
num: 0001  X  X  X  X
num: 0011  X  X  X  X
num: 0201  X  X  X  X
num:
num:
...

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Based on the data given, I should get just the 4 items as shown, but for some reason, each time I attempt to update the AoA, an empty cell gets added. I've included a couple of print Dumper() lines where the problem occurs, but the reason it's occuring eludes me.

Can someone explain what's going on. (and if you know a better way to do this, I'm all ears\eyes)

use strict;
use Data::Dumper;

my @display = (); # AoA
while (<DATA>) {
    build_display($_);
}

print "     SNO   A  B  C  D\n";
for (@display) {
    print 'num: ' . join('  ', @$_) . "\n";
}
print "\n";


##########################
sub build_display {
##########################
    my $serialno = shift;
    chomp $serialno;
    if ($serialno) {
        my ($prefix,$number) = ($serialno =~ /^(\w)(\w{4})/);
        my $j = ($prefix =~ /A/i) ? 1
              : ($prefix =~ /B/i) ? 2
              : ($prefix =~ /C/i) ? 3
              : ($prefix =~ /D/i) ? 4 : 0;

        my $temp = '';
        for (0..$#display) {
            if ($display[$_][0] =~ /^$number$/i) {  ## Need to update 
+array_ref
                $temp = $display[$_];     ## copy to temp
                splice(@display, $_, 1);  ## delete from array. Added 
+to top later.
print "After Delete: " . Dumper(\@display); <stdin>;
            }
        }
## ?? Adds an element to the @display array if update is required. But
+ why OR how ?? 
print "Before Add: " . Dumper(\@display); <stdin>;
        ## if 'number' not in array, create a new entry.
        $temp = [$number,' ',' ',' ',' '] if (!$temp);

        $temp->[$j] = 'X'; ## flag the applicable prefix
        unshift @display, $temp;  ## add to top of array.
    }
}

__DATA__
A0011
B0001
C0201
D0001
A1011
B0201
C1011
D0201
A0201
B0011
C0011
D0011
A0001
B1011
C0001
D1011

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In reply to Populate and sort AoA by nedals

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