How I can flatten a tree in an orderly way? - php

Question

I have PHP array (tree), something like this:
$categoryTree = [
0 => [
'id' => 1360,
'parent' => 0,
'name' => 'main A',
'children' => [
0 => [
'id' => 1361,
'parent' => 1360,
'name' => 'sub a1'
],
1 => [
'id' => 57,
'parent' => 1360,
'name' => 'sub a2'
]
]
],
1 => [
'id' => 10,
'parent' => 0,
'name' => 'Main B'
]
];
I want to convert it into:
$categoryTree = [
0 => [
'id' => 1360,
'parent' => 0,
'name' => 'main A'
],
1 => [
'id' => 1361,
'parent' => 1360,
'name' => 'sub a1'
],
2 => [
'id' => 57,
'parent' => 1360,
'name' => 'sub a2'
],
3 => [
'id' => 10,
'parent' => 0,
'name' => 'Main B'
]
];

Answer 1

It is rather simple. You walk recursively and only make a recursive call if the node has the key children. During the iteration in the foreach loop, keep collecting results in an result array.
<?php
function flatten($tree, &$results){
foreach($tree as $kid){
$kid_copy = $kid;
unset($kid_copy['children']);
$results[] = $kid_copy;
if(isset($kid['children'])) flatten($kid['children'], $results);
}
}
Online Demo

Answer 2

Alternatively, using a generator, which then doesn't need the second argument:
function recurIter($arr) {
foreach ($arr as $item) {
$orig = $item;
unset($item["children"]);
yield $item;
if (isset($orig["children"])) yield from recurIter($orig["children"]);
}
}
$result = iterator_to_array(recurIter($categoryTree), false);