for ($a=0; $a<=$#columns; $a++) {
      for ($b=0; $b<=$#columns; $b++) {
        print "$list[$a][$b] "; # for testing
      }
      print " \n";
   }  

##</code><code>##

my @AoA = ([1, 2, 3], [4, 5, 6], [7, 8, 9]); # an array of arrays for testing purpose
for my $row (@AoA) {
    for my $col (@$row) {
        print "$col ";
    }
    print "\n";
}

##</code><code>##

1 2 3
4 5 6
7 8 9

##</code><code>##

my @AoA = ([1, 2, 3], [4, 5, 6], [7, 8, 9]);
for my $row (@AoA) {
    my ($sum, $count) = (0, 0);
    for my $col (@$row) {
        $sum +=  "$col ";
        $count ++;
    }
    print "Average: ", $sum / $count, "\n" if $count;
}

##</code><code>##

Average: 2
Average: 5
Average: 8