Use recursion to accumulate rows without depending on class property variable - php

Question

Having this array :
[
"id" => 5,
"name" => "Item 5",
"all_parents" => [
"id" => 4,
"name" => "Item 4",
"all_parents" => [
"id" => 3,
"name" => "Item 3",
"all_parents" => [
"id" => 2,
"name" => "Item 2",
"all_parents" => [
"id" => 1,
"name" => "Item 1",
"all_parents" => null
]
]
]
]
]
I created a recursive php function that transform that array to this:
[
["id" => 1, "name" => "Item 1"],
["id" => 2, "name" => "Item 2"],
["id" => 3, "name" => "Item 3"],
["id" => 4, "name" => "Item 4"],
["id" => 5, "name" => "Item 5"],
]
The code is this:
private array $breadcrumb = [];
private function generateBreadcrumb($structure) : array
{
if($structure) {
$this->breadcrumb[] = array(
"id" => $structure['id'],
"name" => $structure['name'],
);
$this->generateBreadcrumb($structure['all_parents'] ?? []);
}
return array_reverse($this->breadcrumb);
}
How can I redesign this method without depending on class property $breadcrumb?

Answer 1

By following your initial code, you could do:
function generateBreadcrumb($structure, &$output = []) : array
{
if ($structure) {
$output[] = array(
"id" => $structure['id'],
"name" => $structure['name'],
);
$this->generateBreadcrumb($structure['all_parents'] ?? [], $output);
}
return array_reverse($output);
}
However it could be improved, at least by avoiding to call array_reverse() each time, but only for the root call.

Answer 2

Instead of implementing a recursive function there is the possibility of using the built-in array_walk_recursive function:
$arr = [
'id' => 5,
'name' => 'Item 5',
'all_parents' => [
'id' => 4,
'name' => 'Item 4',
'all_parents' => [
'id' => 3,
'name' => 'Item 3',
'all_parents' => [
'id' => 2,
'name' => 'Item 2',
'all_parents' => [
'id' => 1,
'name' => 'Item 1',
'all_parents' => null
]
]
]
]
];
function generateBreadcrumb($structure): array {
$retval = [];
array_walk_recursive($structure, function ($item, $key) use (&$retval) {
if ($key === 'id') {
$retval[] = [$key => $item];
} elseif ($key === 'name') {
$retval[array_key_last($retval)][$key] = $item;
}
});
return array_reverse($retval);
}
$result = generateBreadcrumb($arr);
Note that array_walk_recursive only visits leafs, so with the exception of the innermost 'all_parents', the other ones are not visited.
A none-recursive version would be this:
function generateBreadcrumb(array $arr): array {
$retval = [];
$temp = &$arr;
do {
$retval[] = [ 'id' => $temp['id'], 'name' => $temp['name'] ];
$temp = &$temp['all_parents'];
} while ($temp !== null);
return array_reverse($retval);
}

Answer 3

You can accumulate the indeterminate-depth data by merging as you recurse the tree. You do not need to introduce any new variables to carry the data while recursing nor do you need to array_reverse() the returned data.
The below technique will prioritize recursion while $structure['all_parents'] is truthy (not null) and cease recursion once it encounters the null all_parents value in the deepest subarray. From the bottom, the id and name elements will be accessed and merged into the empty or accumulated array of row data.
Code: (Demo)
class Recursing
{
public function generateBreadcrumb(array $structure): array
{
return array_merge(
$structure['all_parents']
? $this->generateBreadcrumb($structure['all_parents'])
: [],
[
['id' => $structure['id'], 'name' => $structure['name']]
]
);
}
}
$test = new Recursing;
var_export($test->generateBreadcrumb($arr));
Output:
array (
0 =>
array (
'id' => 1,
'name' => 'Item 1',
),
1 =>
array (
'id' => 2,
'name' => 'Item 2',
),
2 =>
array (
'id' => 3,
'name' => 'Item 3',
),
3 =>
array (
'id' => 4,
'name' => 'Item 4',
),
4 =>
array (
'id' => 5,
'name' => 'Item 5',
),
)