perl populating hash of hashes recursively - perl

Question

I have a hash like this:
{ ABC => [1, 2],
1 => [11, 12,13,14],
13 => [17,20] }
I want to generate a hash of hashes like this:
(ABC => { 1 => {11 => {},
12 => {},
13 => { 17 => {}
20 = {} },
14 => {}
},
2 => {}
}
)
The above hash is nothing but a tree with a root node and further child nodes.
I understand we have to use recursion to check child nodes for every parent node. I have looked at the question previously asked here. I am unable to understand how during recursion specific node's data is stored under its particular parent key. In other words how can hash of hashes be populated recursively ?
Appreciate any pointers or explanation.
Thanks for your time

Answer 1

The real problem is that you don't really know what you want.
{ABC => 1 => 11 => {}
=> 1 => 12 => {}
=> 1 => 13 => 17 => {}
=> 20 = {}
=> 1 => 14 => {}
}
is just a really weird way of writing
{
ABC => "1",
11 => {},
1 => "12",
{} => "1",
13 => "17",
{} => "20",
{} => "1",
14 => {},
}
That makes no sense. I think you actually want
{
ABC => {
1 => {
11 => {},
12 => {},
13 => {
17 => {},
20 => {},
},
14 => {},
},
},
}
Now that you know what you want, you should take a stab at implementing it.

Answer 2

You can use the code I defined here: How can I merge several hashes into one hash in Perl?
having defined #hash_list so:
my #hash_list
= { map { ref() eq 'ARRAY' ? { map {; $_ => {} } #$_ } : $_ }
%{{ ABC => [1, 2]
, 1 => [11, 12,13,14]
, 13 => [17,20]
}}
};

Answer 3

#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper;
my %data = (
ABC => [1, 2],
1 => [11, 12, 13, 14],
13 => [17, 20]
);
my %hash;
sub modify_hash {
my ($base, $ref) = #_;
for my $k (keys %$ref) {
if (exists $base->{$k}) {
$ref->{$k} = $base->{$k};
delete $base->{$k};
}
modify_hash($base, $ref->{$k});
}
}
map { %{$hash{$_}} = map { $_ => {}; } #{$data{$_}}; } keys %data;
map { modify_hash(\%hash, $hash{$_}); } keys %hash;
print Dumper(\%hash);
output:
$VAR1 = {
'ABC' => {
'1' => {
'11' => {},
'13' => {
'17' => {},
'20' => {}
},
'12' => {},
'14' => {}
},
'2' => {}
}
};