How to address specific array element in complex data structure in 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?

You can address the hash in the array (element 0) like this: $data{profiles}{Tags}[0]{"###PLACEHOLDER###"} = "data" — Håkon Hægland
– Håkon Hægland, Commented May 13, 2019 at 12:26
But this is an array and the values are not sorted so I cant be sure to get the correct one. — Mister Lamp
– Mister Lamp, Commented May 13, 2019 at 12:30
can you save the correct index (into the array) in a variable? — Håkon Hægland
– Håkon Hægland, Commented May 13, 2019 at 12:33
I would advise you to create an object oriented class for such a complex nested data structure, then provide methods which allow you to add data in a manner that suits the semantics of your object. — TFBW
– TFBW, Commented May 13, 2019 at 12:35

Diab Jerius · Accepted Answer · 2019-05-15 17:54:40Z

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###'
        ];

edited May 15, 2019 at 17:54

answered May 13, 2019 at 14:06

Diab Jerius

2,32014 silver badges18 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Diab Jerius Over a year ago

It does on my machine. What does it do on your machine?

Diab Jerius Over a year ago

Right. Good catch. Nested references to the structures. I'll fix that. If the OP wants to directly change the ###PLACEHOLDER### string they'll still need a reference to the value. [Now I see what I did. I switched dpathr with dpath for the two cases when I was creating the post. Ooops]

ikegami · Accepted Answer · 2019-05-13 23:22:39Z

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,
                },
              ],
}

Collectives™ on Stack Overflow

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

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related