Greetings Fellow Monks, Monkettes & Monkees...

I was writing a program today and hit upon a Perl question I've never thought about before. Suppose I have some sort of hash structure (such as the one in my example below) and I would like to "reach in" and manipulate one of the nested hashes and that I know the necessary keys and in the correct order, but I only have them in an array form (i.e., qw/level1key level2key.../ etc.) What is the best method to return a reference from the hash using an array of keys?

I have constructed the following example which seems to work acceptably, but my question is: "Is the only and/or best approach to solve the problem?"

(Btw, the hash in the example is completely arbitrary and has no real-world significance)

Thanks

Jwhitten

#! /bin/perl

use Data::Dumper;

my $hash = {
        'wheels' => {
                'four' => {
                        'car' => {
                                'plain' => {
                                        'sporty' => 'honda',
                                        'retro' => 'volkswagon',
                                        },
                                'fancy' => {
                                        'red' => 'ferrari',
                                        'silver' => 'maserati',
                                        },
                                },
                        'truck' => {
                                'light' => {
                                        'chevy' => 'pickup',
                                        },
                                'utility' => {
                                        'us' => 'mail',
                                        'city' => 'trash',
                                        'muni' => 'power',
                                        },
                                },
                        },
                'one' => 'Unicycle',
                'two' => {
                        'pedals' => 'bicycle',
                        'motorized' => 'motorcycle',
                        },
                'three' => 'tricycle',
                },
        };


##---------------------------
## DEEP REFERENCE
##---------------------------

fetch($hash, 'wheels');
fetch($hash, 'wheels', 'one');
fetch($hash, 'wheels', 'four', 'truck', 'utility');
fetch($hash, 'wheels', 'four', 'truck', 'utility', 'blah'); # doesn't 
+exist

sub fetch {
        my ($hash, @keys) = @_;
        print "==> Fetching [" . join(', ', @keys) . ']' . "\n";
        my $results = deep_reference($hash, @keys);
        print Dumper($results), "\n\n";
        }

sub deep_reference {
        my ($hash, @keys) = @_;
        my $ref = undef;
        my $code = '$hash->' . join('->', map { "{$_}" } @keys);
        return eval $code;
        }
[download]

Produces:

==> Fetching [wheels]
$VAR1 = {
          'three' => 'tricycle',
          'one' => 'Unicycle',
          'two' => {
                     'pedals' => 'bicycle',
                     'motorized' => 'motorcycle'
                   },
          'four' => {
                      'car' => {
                                 'plain' => {
                                              'sporty' => 'honda',
                                              'retro' => 'volkswagon'
                                            },
                                 'fancy' => {
                                              'silver' => 'maserati',
                                              'red' => 'ferrari'
                                            }
                               },
                      'truck' => {
                                   'light' => {
                                                'chevy' => 'pickup'
                                              },
                                   'utility' => {
                                                  'city' => 'trash',
                                                  'muni' => 'power',
                                                  'us' => 'mail'
                                                }
                                 }
                    }
        };


==> Fetching [wheels, one]
$VAR1 = 'Unicycle';


==> Fetching [wheels, four, truck, utility]
$VAR1 = {
          'city' => 'trash',
          'muni' => 'power',
          'us' => 'mail'
        };


==> Fetching [wheels, four, truck, utility, blah]
$VAR1 = undef;
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.