How do I sort hash of hashes by a sub key/value using perl? - perl

Question

I would like sort the following Hash. parentXX should be sort with the value of __displayorder, the Xtopic of a parent and Xprod of a topic should sort alphabeticly.
$VAR1 = {
'views' => {
'parent23' => {
'__displayorder' => 2,
'vtopic1' => {
'gprod1.1' => undef,
'aprod1.2' => undef,
},
'btopic2' => {
'tprod2.1' => undef,
'mprod2.2' => undef,
},
},
'parent98' => {
'__displayorder' => 1,
'atopic1' => {
'qprod1.1' => undef,
'jprod1.2' => undef,
},
'xtopic2' => {
'kprod2.1' => undef,
'fprod2.2' => undef,
}
}
}
}

Answer 1

You can't sort a hash. Can you make do with having the names of the views in the specific order?
my $views = $VAR1->{views};
my #sorted_view_keys = sort {
$views->{$a}{__displayorder} cmp $views->{$b}{__displayorder}
} keys(%$views);
Or maybe you want the sorted views?
my #sorted_views = map { $views->{$_} } #sorted_view_keys;
-or-
my #sorted_views = #$views[#sorted_view_keys];

Answer 2

As already mentioned, you can't sort a normal Perl hash. Perl hashes are unordered. But you can use the CPAN module Tie::IxHash to get an ordered hash. The lines below transform all the sub-hashes from your sample output into Tie::IxHash hashes and do some sorting (e.g. alphabetically or by display order):
use Tie::IxHash;
my $views = $VAR1->{views};
while(my($view_key, $view) = each %$views) {
while(my($topic, $prods) = each %$view) {
next if $topic =~ m{^__};
tie my %new_prods, 'Tie::IxHash', (map { ($_ => $prods->{$_}) } sort keys %$prods);
$view->{$topic} = \%new_prods;
}
tie my %new_view, 'Tie::IxHash', (map { ($_ => $view->{$_}) } sort keys %$view);
$views->{$view_key} = \%new_view;
}
tie my %new_views, 'Tie::IxHash', (map { ($_ => $views->{$_}) } sort { $views->{$a}->{__displayorder} <=> $views->{$b}->{__displayorder} } keys %$views);
$VAR1->{views} = \%new_views;