Creating multidimensional array and removing empty categories - php

Question

I have a single-dimensional array of categories; some of which are children of other categories, and some of which contain 'elements'. I need to turn it into a multidimensional array, and remove any categories which have no elements in them or any of their children (or children's children...).
I have the following array:
$category_array = array(
1 => array(
'elementcount' => 3,
'parentcat' => 0,
'depth' => 1
),
4 => array(
'elementcount' => 0,
'parentcat' => 1,
'depth' => 2
),
8 => array(
'elementcount' => 0,
'parentcat' => 4,
'depth' => 3
),
9 => array(
'elementcount' => 2,
'parentcat' => 4,
'depth' => 3
),
11 => array(
'elementcount' => 3,
'parentcat' => 0,
'depth' => 1
),
12 => array(
'elementcount' => 0,
'parentcat' => 11,
'depth' => 2
),
21 => array(
'elementcount' => 3,
'parentcat' => 0,
'depth' => 1
)
);
and I need the following array:
$multidimensional_array = array(
1 => array(
'elementcount' => 3,
'children' => array(
4 => array(
'elementcount' => 0,
'children' => array(
9 => array(
'elementcount' => 2
)
)
)
)
),
11 => array(
'elementcount' => 3,
),
21 => array(
'elementcount' => 3,
)
);
How can this be achieved?

Answer 1

This would be an approach:
<?php
$input = [
1 => [
'elementcount' => 3,
'parentcat' => 0,
'depth' => 1
],
4 => [
'elementcount' => 0,
'parentcat' => 1,
'depth' => 2
],
8 => [
'elementcount' => 0,
'parentcat' => 4,
'depth' => 3
],
9 => [
'elementcount' => 2,
'parentcat' => 4,
'depth' => 3
],
11 => [
'elementcount' => 3,
'parentcat' => 0,
'depth' => 1
],
12 => [
'elementcount' => 0,
'parentcat' => 11,
'depth' => 2
],
21 => [
'elementcount' => 3,
'parentcat' => 0,
'depth' => 1
]
];
$maxDepth = max(array_column($input, 'depth'));
// handle elements from higher to lower depth
for ($d = $maxDepth; $d >= 0; $d--) {
array_walk($input, function(&$entry, $index) use (&$input, $d) {
if (isset($entry['depth']) && $entry['depth'] == $d) {
// omit entries without elements or elements in children
if ($entry['elementcount'] < 1 && empty($entry['children'])) {
unset($input[$index]);
// handle as child entry of a parent entry
} else if (array_key_exists($entry['parentcat'], $input)) {
$input[$entry['parentcat']]['children'][$index] = [
'elementcount' => $entry['elementcount'],
'children' => isset($entry['children']) ? $entry['children'] : []
];
unset($input[$index]);
// handle as ordinary entry
} else {
$input[$index] = [
'elementcount' => $entry['elementcount'],
'children' => isset($entry['children']) ? $entry['children'] : []
];
}
}
});
}
print_r($input);
The strategy:
handle higher depths first so that the order of input elements does not matter
for each element check if the parent exists, if so stuff it in there
redefine all handled elements
The obvious output is:
(
[1] => Array
(
[elementcount] => 3
[children] => Array
(
[4] => Array
(
[elementcount] => 0
[children] => Array
(
[9] => Array
(
[elementcount] => 2
[children] => Array
(
)
)
)
)
)
)
[11] => Array
(
[elementcount] => 3
[children] => Array
(
)
)
[21] => Array
(
[elementcount] => 3
[children] => Array
(
)
)
)
I took the liberty to create a slightly modified result compared to your suggestion:
The 'children' property always exists as an array. That makes the usage of the result easier and more robust later on. I'd say that in general all elements inside a structure should have identical structure themselves if possible ...

Answer 2

function isParent($id, $list) : bool {
foreach($list as $item) {
if ($item['parentcat'] === $id) {
return true;
}
}
return false;
}
function buildLevel($parent, $catsByParent) : array {
$result = $catsByParent[$parent] ?? [];
foreach($result as $id => $cat) {
if (isset($catsByParent[$id])) {
$result[$id]['children'] = buildLevel($id, $catsByParent);
unset($catsByParent[$id]);
}
}
return $result;
}
// Filter out empty categories
$cats = array_filter(
$category_array,
function($cat, $id) use($category_array) {
return $cat['elementcount']>0 || isParent($id, $category_array);
},
ARRAY_FILTER_USE_BOTH
);
$catsByParent = [];
// Build cats list keyed by parentcat
foreach($cats as $id => $cat) {
$parent = $cat['parentcat'];
unset($cat['parentcat'], $cat['depth']);
$catsByParent[$parent] = ($catsByParent[$parent] ?? []) + [$id => $cat];
}
// Build result
$multidimensional_array = buildLevel(0, $catsByParent);
print_r($multidimensional_array);
First one filters out empty elements, i.e "categories which have no elements in them or any of their children". (children's children requirement sounds strange, wouldn't that be "any of their children" one level further down?)
Then the remaining categories are grouped/sorted by parentcat, aka "level id", to make the list workable :).
Then that list is traversed, starting with level id 0 at the top, and recursively processed(the children) as deep down as needed.