unknown number of dimensions of a multidimensional hash

[Otogi]

This most probably has been answered before but can't come up with the right keys to research it. I want to dynamically create a hash with multiple dimensions (number of dimensions dynamically increase) for example:

$data {$a}{$b}
$data {$a}{$b}{$c}
$data {$d}{$e}

So as the script is running I could add more dimensions to the initial hash using a subroutine called given the initial  $data{$a} . How do I do that? and how would I read the hash to get the keys and values if I don't know the dimension of the hash. Thank you.

[GrandFather]

The following code is taken from a game engine and manipulates "keys" of the form (\w+\.)+\w+. Each word represents a hash level.

our %GameState; # The entire game context

# looks up a key (passed as the first param) and adds the value
# (if provided as second param). Returns a reference to the value
# list.
sub Entity {
  my ($key, $value) = @_;
  return undef if ! defined $key;
  my $hash = \%GameGlobals::GameState;
  my @keys = split /\./, $key;

  map {$_ = lc $_} @keys;
  while (@keys && defined $hash) {
    my $key = shift @keys;
    if (@keys) {
      $hash->{$key} = {} if ! exists $hash->{$key};
      $hash = $hash->{$key};
    } else {
      $hash->{$key} = [] if ! exists $hash->{$key};
      push @{$hash->{$key}}, $_[1] if defined $value;
      return \$hash->{$key};
    }
  }
}

[duff]

Another thing you can do is use concatenated keys rather than a multidimensional data structure. (I don't know how critical the hierarchical nature is to your problem solution) That is, instead of:

$data {$a}{$b}
$data {$a}{$b}{$c}
$data {$d}{$e}

you would use

$data{join "\0", $a, $b}
$data{join "\0", $a, $b, $c}
$data{join "\0", $d, $e}

Then to access the keys you'd use your standard keys operator:

for (keys %data) {
   # you could do something with $data{$_} directly,
   # or if you need access to the individual keys ...
   my @keys = split /\0/;
   # ...
}

The main caveat is that your "key separator" should be something that doesn't appear in your keys. I chose "\0" in this example assuming that your keys aren't likely to contain NUL bytes.

[Anonymous Monk]

If the hash is not ragged, you simply know its dimensionality. If you somehow lose this information

sub hashfirst { $_[0]->{($_) = keys %{$_[0]}} }
sub shape {
  my $h = shift;
  my @s;
  for (;'HASH' ne ref $h; $h = hashfirst($h)) {
    push @s, scalar(keys %$h);
  }
  @s
}

may help you remember. This feels like an X-Y question.