Collection

The Elementor\Core\Utils\Collection class provide a fluent, convenient wrapper for working with arrays of data. The idea is to transform the use of foreach, for or php built it functions with the Collection class, basically to make the code more readable.

The class is heavily inspire by the Laravel Collection, it is recommended to read the laravel docs to understand the concept of collections: Laravel Docs. Another great resource, if videos are your cup of tea, this talk by Adam Wathan: Curing the common loop .

Example:

php

use Elementor\Core\Utils\Collection;
use Elementor\Core\Base\Document;

$only_parent_documents = ( new Collection( $data ) )
    ->map( function ( Document $document ) {
        return $document->get_main_id();
    })
    ->unique()
    ->values();

Same result without Collection:

php

use Elementor\Core\Base\Document;

$only_parent_documents = [];

/** @var Document $document */
foreach( $data as $document ) {
    $id = $document->get_main_id();

    if ( in_array( $id, $only_parent_documents, true ) ) {
        continue;
    }
    
    $only_parent_documents[] = $id;
}

Another option:

php

use Elementor\Core\Base\Document;

$only_parent_documents = array_unique(
    array_map( function ( Document $document ) {
        return $document->get_main_id();
    }, $data ) 
);

Extend Collection

There are two ways to extend the Collection class, you can add your new method to class itself, or you can extend the Collection and create more specific Collection class, for example Documents_Collection:

php

use Elementor\Core\Utils\Collection;
use Elementor\Core\Base\Document;

class Documents_Collection extends Collection {
    public function parent_document_ids() {
        return $this->map( function ( Document $document ) {
            return $document->get_main_id();
        })
        ->unique();
    }
}

usage:

php

$ids = ( new Documents_Collection( $data ) )
    ->parent_document_ids()
    ->values();