Loop through every occurrence of specific child key in a nested structure - php

Question

I have this payload,
[
{
"id": 1,
"name": "T-Shirt",
"children_rec": [
{
"id": 2,
"name": "Classic",
"children_rec": [
{
"id": 3,
"name": "Lycra",
"children_rec": []
}
]
},
{
"id": 4,
"name": "Plain",
"children_rec": []
}
]
},
{
"id": 5,
"name": "Shirt",
"children_rec": [
{
"id": 6,
"name": "Plain",
"children_rec": []
}
]
}
]
I want to loop through every occurrence of children_rec.
What I have tried is,
foreach ($mainCategories as $category) {
if (!empty($category['children_rec'])) {
foreach ($category['children_rec'] as $child) {
if (!empty($category['children_rec'])) {
var_dump($child);
}
}
}
}
But this is not the dynamic way to achieve this. What if I have 5 or 6 level of childer_rec. How can I achieve this?
Edit
#ggorlen's way is cool, but What if I need this output?
[
{
"id": 1,
"name": "T-Shirt",
"children": [
"2",
"3",
"4"
]
},
{
"id": 5,
"name": "Shirt",
"children": [
"6"
]
}
]

Answer 1

Since you don't know the depth, you'll need a stack or recursion. Here's a solution with a stack:
<?php
$tree = json_decode('[ { "id": 1, "name": "T-Shirt", "children_rec": [ { "id": 2, "name": "Classic", "children_rec": [ { "id": 3, "name": "Lycra", "children_rec": [] } ] }, { "id": 4, "name": "Plain", "children_rec": [] } ] }, { "id": 5, "name": "Shirt", "children_rec": [ { "id": 6, "name": "Plain", "children_rec": [] } ] } ]', true);
for ($stack = $tree; !empty($stack);) {
$curr = array_pop($stack);
$flattened[] = $curr["name"]; // or just $curr if you only want the node
if (!empty($curr["children_rec"])) {
array_push($stack, ...$curr["children_rec"]);
}
}
print_r($flattened);
Array
(
[0] => Shirt
[1] => Plain
[2] => T-Shirt
[3] => Plain
[4] => Classic
[5] => Lycra
)
If order is important, you can array_reverse all arrays as you push them onto the stack without harming the linear time complexity.
For the updated specification, just plop the above code into a function and call it for each root node:
<?php
function flatten($tree) {
for ($stack = array_reverse($tree); !empty($stack);) {
$curr = array_pop($stack);
$flattened[] = $curr["id"];
if (!empty($curr["children_rec"])) {
array_push($stack, ...array_reverse($curr["children_rec"]));
}
}
return $flattened;
}
$tree = json_decode('[ { "id": 1, "name": "T-Shirt", "children_rec": [ { "id": 2, "name": "Classic", "children_rec": [ { "id": 3, "name": "Lycra", "children_rec": [] } ] }, { "id": 4, "name": "Plain", "children_rec": [] } ] }, { "id": 5, "name": "Shirt", "children_rec": [ { "id": 6, "name": "Plain", "children_rec": [] } ] } ]', true);
foreach ($tree as &$root) {
$root["children"] = flatten($root["children_rec"]);
unset($root["children_rec"]);
}
echo json_encode($tree, JSON_PRETTY_PRINT)."\n";
Output:
[
{
"id": 1,
"name": "T-Shirt",
"children": [
2,
3,
4
]
},
{
"id": 5,
"name": "Shirt",
"children": [
6
]
}
]