How to generate a tree-like array from flat array without use of references

Question

I'm stuck with transforming flat array to multidimensional tree like. I have already done it, but I used references, which creates another set of problems down the line, so I need to do this without references.

Input array:

Array
[
1 =>[
        'content_id' => 1,
        'sort_order' => 1,
        'level' => 1
    ],
2 =>[
        'content_id' => 7,
        'sort_order' => 2,
        'level' => 2
    ],
3 =>[
        'content_id' => 4,
        'sort_order' => 3,
        'level' => 2
    ],
4 =>[
        'content_id' => 2,
        'sort_order' => 4,
        'level' => 3
    ],
5 =>[
        'content_id' => 3,
        'sort_order' => 5,
        'level' => 1
    ],
6 =>[
        'content_id' => 6,
        'sort_order' => 6,
        'level' => 1
    ],
7 =>[
        'content_id' => 5,
        'sort_order' => 7,
        'level' => 2
    ]
]

Output array:

1 => [
    'id' = 1,
    'visited' = 0,
    'children' => [
             2 => [
                  'id' => 7,
                  'visited' => 0,
                  'children' => []
             ],
             3 => [
                  'id' => 4,
                  'visited' => 0,
                  'children' => [
                           4 => [
                                'id' = 2,
                                'visited' = 0,
                                'children' => []
                           ]
             ]
],
5 => [
     'id' => 3,
     'visited' => 0,
     'children' => []
],
6 => [
     'id' => 6,
     'visited' => 0,
     'children' => [
             7 => [
                  'id' => 5,
                  'visited' => 0,
                  'children => []
             ]
]
]

Any idea how to tackle a problem like this without having direct parent relation set? I can use recursion, but references are problem.

I dont see corelation between building tree-like array without reference question and fixing already written stuff that is using references question.. — SubjectX
– SubjectX, Commented Jul 28, 2015 at 11:45
Your array makes no sense to me. Can you please try using valid PHP syntax in your example code? — Sherif
– Sherif, Commented Jul 28, 2015 at 11:46

Plenka · Accepted Answer · 2015-07-28 12:46:42Z

1

Oooh, this kind of problems do tickle my fancy. So, here is my solution:

<?php

$origArray = array(
    array('content_id' => 1, 'sort_order' => 1, 'level' => 1),
    array('content_id' => 7, 'sort_order' => 2, 'level' => 2),
    array('content_id' => 4, 'sort_order' => 3, 'level' => 2),
    array('content_id' => 2, 'sort_order' => 4, 'level' => 3),
    array('content_id' => 3, 'sort_order' => 5, 'level' => 1),
    array('content_id' => 6, 'sort_order' => 6, 'level' => 1),
    array('content_id' => 5, 'sort_order' => 7, 'level' => 2),
);

function sortByOrder($a, $b) {
    if ($a['sort_order'] == $b['sort_order']) {
        return 0;
    }
    return ($a['sort_order'] < $b['sort_order']) ? -1 : 1;
}

function createHierarchicalArray($arr) {
    $result = array();
    foreach ($arr as $el) {
        $result = insertArrayElement($result, $el['content_id'], $el['level']);
    }
    return $result;
}

function insertArrayElement($array, $id, $level, $currentLevel = 1) {
    if ($level > $currentLevel) {
        $ids = array_keys($array);
        $currentId = end($ids);
        if (!isset($array[$currentId]['children'])) {
            $array[$currentId]['children'] = array();
        }
        $array[$currentId]['children'] = insertArrayElement($array[$currentId]['children'], $id, $level, $currentLevel + 1);
    } else {
        $array[$id] = array();
    }

    return $array;
}

// Could do without this, if the array is already sorted. Otherwise it's a necessary step.
uasort($origArray, 'sortByOrder');

$result = createHierarchicalArray($origArray);

var_dump($result);

Edit: Changed the code to incorporate the changes in the question.

edited Jul 28, 2015 at 12:46

answered Jul 28, 2015 at 12:00

Plenka

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5 Comments

SubjectX Over a year ago

Sorry if I changed something that gave you problem, was hoping only visual representation got changed with my edits.

SubjectX Over a year ago

Nice work man, really fast! Is there a way to keep the other data from original elements put into new array? I mean, I would probably pass the id of element from original array to recursive function and then copy stuff from original array in that $array['$id] = array() line. Is there a better/safer way?

SubjectX Over a year ago

$currentKey should probably be $currentId. Also, how do we get rid of notice: "Only variables should be passed by reference"?

Plenka Over a year ago

I'd pass the contents of the original array to the insertArrayElement function as well (probably as the fourth parameter) and change the $array[$id] = array(); line to $array[$id] = $el; (or whatever you decide to call the parameter). I've changed the $currentId = end(array_keys($array)); line to get rid of the reference passing notice.

SubjectX Over a year ago

Thank you again for quick and really clean solution.

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