Traversing a multi-dimensional hash in Perl

Question

If you have a hash (or reference to a hash) in perl with many dimensions and you want to iterate across all values, what's the best way to do it. In other words, if we have $f->{$x}{$y}, I want something like

foreach ($x, $y) (deep_keys %{$f})
{
}

instead of

foreach $x (keys %f) 
    {
    foreach $y (keys %{$f->{$x}) 
    {
    }
}

Answer 1

Stage one: don't reinvent the wheel :)

A quick search on CPAN throws up the incredibly useful Data::Walk. Define a subroutine to process each node, and you're sorted

use Data::Walk;

my $data = { # some complex hash/array mess };

sub process {
   print "current node $_\n";
}

walk \&process, $data;

And Bob's your uncle. Note that if you want to pass it a hash to walk, you'll need to pass a reference to it (see perldoc perlref), as follows (otherwise it'll try and process your hash keys as well!):

walk \&process, \%hash;

For a more comprehensive solution (but harder to find at first glance in CPAN), use Data::Visitor::Callback or its parent module - this has the advantage of giving you finer control of what you do, and (just for extra street cred) is written using Moose.