How to extract part of multidimensional array tree with PHP - php

Question

I have a huge dynamically generated tree. The tree is generated from a flat array based on each elements "parent_id" attribute.
The final result would for example look like this:
Array
(
[0] => Array
(
[id] => 70
[name] => Top Corp
[parent_id] => 0
[children] => Array
(
[0] => Array
(
[id] => 43
[name] => Department
[parent_id] => 70
[children] => Array
(
[0] => Array
(
[id] => 45
[name] => Building
[parent_id] => 43
[children] => Array
(
[0] => Array
(
[id] => 75
[name] => Office
[parent_id] => 45
)
)
)
How do I extract just a part of the array tree? What functions or methods should I look at?
E.g. how do I say another sub-level (potentially 20-30 levels deep) is now the top.
For example, a pseudo function of sliceTree(45) should produce the following result, aka start the tree from id 45
[0] => Array
(
[id] => 45
[name] => Building
[parent_id] => 43
[children] => Array
(
[0] => Array
(
[id] => 75
[name] => Office
[parent_id] => 45
)
)
)
There is no way to know how deep the tree can go so it a solution needs to be recursive.
I have tried looping the array, looking for the starting id, but I am unsure of how to continue the execution after the point has been found.
My proposed solution is as follows
function sliceTree($tree, $id){
$ret = [];
foreach ($tree as $out) {
// if the top level matches
if($out["id"] == $id){
array_push($ret, $out);
}
else {
if(isset($out["children"])){
foreach ($out["children"] as $c) {
if($c["id"] == $id){
array_push($ret, $c);
}
// probably needs to call itself here
}
}
}
}
return $ret;
}
Which works, but only for top-level elements. How can I make recursive and account for the many levels of children?

Answer 1

The sliceTree() function basically looks for a certain id and returns it. Something like this:
function sliceTree($tree, $branchId)
{
// check all branches
foreach ($tree as $branch) {
// have we found the correct branch?
if ($branch['id'] == $branchId) return $branch;
// check the children
if (isset($branch['children'])) {
$slice = sliceTree($branch['children'], $branchId);
if (isset($slice)) return $slice;
}
}
// nothing was found
return null;
}
As you can see, this routine is recursive. Code is untested.
I'm sorry about the mixed metaphors: branches and children, but you started it.
This function is slightly more complex, than I would like it to be, because in your example the children key is absent when there are no children. I would normally expect it to be there and the value to be an empty array.