Programming Perl, 4th Edition

Generation of a Hash of Complex Records

Because Perl is quite good at parsing complex data structures, you might just put your data declarations in a separate file as regular Perl code, and then load them in with the do or require built-in functions. Another popular approach is to use a CPAN module (such as XML::Parser) to load in arbitrary data structures expressed in some other language (such as XML).

You can build data structures piecemeal:

$rec = {};
$rec–>{series} = "flintstones";
$rec–>{nights} = [ find_days() ];

Or read them in from a file (here, assumed to be in field=value syntax):

@members = ();
while (<>) {
     %fields = split /[\s=]+/;
     push @members, { %fields };
}
$rec–>{members} = [ @members ];

And fold them into larger data structures keyed by one of the subfields:

$TV{ $rec–>{series} } = $rec;

You can use extra pointer fields to avoid duplicate data. For example, you might want a "kids" field included in a person’s record, which might be a reference to an array containing references to the kids’ own records. By having parts of your data structure refer to other parts, you avoid the data skew that would result from updating the data in one place but not in another:

for $family (keys %TV) {
    my $rec = $TV{$family};   # temporary pointer
    @kids = ();
    for $person ( @{$rec–>{members}} ) {
        if ($person–>{role} =~ /kid|son|daughter/) {
            push @kids, $person;
        }
    }
    # $rec and $TV{$family} point to same data!
    $rec–>{kids} = [ @kids ];
}

The $rec–>{kids} = [ @kids ] assignment copies the array ...