How to address specific array element in complex data structure in perl - perl

Question

I have a complex json data structure in perl like in the following example. I want to address an array element and store data.
Variable
$VAR1 = {
'dummy' => 'foo',
'profiles' => {
'Tags' => [
{
'###PLACEHOLDER###',
}
],
}
I can for example add an element at "###PLACEHOLDER###" but want later in the perl script to add beneath that Placeholder additional information.
Normally i would address these elements with $var->{profiles}->{Tags}->{PLACEHOLDER} but this is not working with an array.
I dont want to create everytime a foreach loop when i know the name exactly.
Any advice?

Answer 1

[UPDATE: used dpathr instead of dpath for the references to structures]
[UPDATE: used dpath instead of dpathr for the references to elements]
Data::DPath can do what you require. Here's code which returns a reference to any structure (hash or array) which contains an element whose value is ###PLACEHOLDER###:
use strict;
use warnings;
use Data::Dumper;
use Data::DPath qw[ dpath dpathr ];
my $struct = {
'dummy' => 'foo',
'profiles' => {
'ARRAY' => [ '###PLACEHOLDER###' ],
'HASH' => { key => '###PLACEHOLDER###' },
},
};
my $path = dpath( '//[value eq "###PLACEHOLDER###"]/..' );
my #matches = $path->match( $struct );
print Dumper \#matches;
It results in:
$VAR1 = [
[
'###PLACEHOLDER###'
],
{
'key' => '###PLACEHOLDER###'
}
];
If you want direct access to the element, change the path to
my $path = dpathr( '//*[value eq "###PLACEHOLDER###"]' );
with the result:
$VAR1 = [
\'###PLACEHOLDER###',
\'###PLACEHOLDER###'
];

Answer 2

It's not clear to me what you what "adding an element at ###PLACEHOLDER###" means. Elements can be added to arrays and hashes, and it's not clear to which array or hash you are referring.
To append an element to the array referenced by $var->{profiles}{Tags}, use
push #{ $var->{profiles}{Tags} }, $val;
This results in
$VAR1 = {
'dummy' => 'foo',
'profiles' => {
'Tags' => [
{
'###PLACEHOLDER###' => undef,
},
$val
],
}
To add an element to the hash referenced by the last element of the array referenced by $var->{profiles}{Tags}, use
$var->{profiles}{Tags}[-1]{$key} = $val;
This results in
$VAR1 = {
'dummy' => 'foo',
'profiles' => {
'Tags' => [
{
'###PLACEHOLDER###' => undef,
$key => $val,
},
],
}
Of course, if $key is ###PLACEHOLDER###, this results in
$VAR1 = {
'dummy' => 'foo',
'profiles' => {
'Tags' => [
{
'###PLACEHOLDER###' => $val,
},
],
}