What is the most efficient way to change a list to a nested object in php

Question

I have a list of (the result of a query in DB) like this:

[
    {
        "id": "1",
        "parent_id": null,
        "title": "مدادنوکی",
        "url": "/medadnoki"
    },
    {
        "id": "2",
        "parent_id": null,
        "title": "جامعه",
        "url": "/commiunity"
    },
    {
        "id": "5",
        "parent_id": "1",
        "title": "درباره ی مدادنوکی",
        "url": "/about"
    },
    {
        "id": "6",
        "parent_id": "1",
        "title": "درباره ی مدادنوکی",
        "url": "/about"
    },
    {
        "id": "7",
        "parent_id": "2",
        "title": "همکاران",
        "url": "/co-worker"
    },
    {
        "id": "8",
        "parent_id": "2",
        "title": "اساتید",
        "url": "/masters"
    }
]

But I want to create an object like this:

[
                {
                    "title": "مدادنوکی",
                    "url": "/medadnoki",
                    "subs" : [
                        {
                            "title": "درباره مدادنوکی",
                            "url": "/about"
                        },
                        {
                            "title": "درباره مدادنوکی",
                            "url": "/about"
                        },
                        {
                            "title": "درباره مدادنوکی",
                            "url": "/about"
                        },
                        {
                            "title": "درباره مدادنوکی",
                            "url": "/about"
                        }
                    ]
                },
                {
                    "title": "جامعه",
                    "url": "/soc",
                    "subs" : [
                        {
                            "title": "همکاران",
                            "url": "/co-work"
                        },
                        {
                            "title": "اساتید",
                            "url": "/masters"
                        }
                    ]
                }
            ]

I have handled this process with two foreach in php and it means I process data twice and it is not efficient and will be slow. Is there any Idea to doing this with just one foreach ? using one foreach means faster than two foreach twice and It will show the result in big data

Answer 1

Assuming you have the results in an order where the parents appear in the results before any children they may have, this should work:

$nested = [];
foreach($results as $r) {
  if($r['parent_id'] === null) {
    $nested[$r['id']] = [
      'title' => $r['title'],
      'url'   => $r['url'],
      'subs'  => []
    ];
    continue;
  }
  $nested[$r['parent_id']]['subs'][] = [
    'title' => $r['title'],
    'url'   => $r['url']
  ];
}
$nested = array_values($nested);