use 5.026;
use warnings;

use Data::Dumper;

my $numX = 5;
my $numY = 7;

my $key = q{a};
my %posns =
   map {
           my $y = $_;
           map {
                   my $x = $_;
                   $key ++ => [ $x, $y ]
               } 0 .. $numX - 1 ;
       } 0 .. $numY - 1;

my $rcKeySorter = sub {
   my $rhPosns = shift;
   my @sortOrder =
      map { unpack q{x4a*}, $_ }
      sort
      map { pack q{Na*}, length, $_ }
      keys %{ $rhPosns };
   return \ @sortOrder;
   };

print Data::Dumper
   ->new( [ \ %posns ], [ qw{ *posns } ] )
   ->Sortkeys( $rcKeySorter )
   ->Dumpxs();