How to build a "child-parent" tree/nested array from database? - php

Question

TABLE `people`
+----+------------+-------+
| sn | name | upper |
+----+------------+-------+
| 1 | Clement | 0 |
| 2 | Jean | 1 |
| 3 | Annie | 1 |
| 4 | Yuan | 2 |
| 5 | Mei | 2 |
| 6 | Blue | 3 |
| 7 | Yang | 5 |
| 8 | Lorinda | 0 |
+----+------------+-------+
The structure is like:
Clement
Jean
Yuan
Mei
Yang
Annie
Blue
Lorinda
The column upper states the upper person of himself/herself.
The problem is: How can I get a nested/multi-dimensional array from MySQL?
I thought I could use loops to fetch, but I failed to automated fetch all the lowers.
The array could be like this:
Array
(
[1]=>Array
(
[self]=>Clement
[2]=>Array
(
[self]=>Jean
[4]=>Array
(
[self]=>Yuan
)
[5]=>Array
(
[self]=>Mei
[7]=>Array
(
[self]=>Yang
)
)
)
[3]=>Array
(
[self]=>Annie
[6]=>Array
(
[self]=>Blue
)
)
)
[8]=>Array
(
[self]=>Lorinda
)
)
Since we don't know how many 'upper' persons does one have, the solution should be an automated function that build a complete array, not just for three or four dimension.
In other word, the function should deep into all the lower person from a top person.

Answer 1

Given your input as:
$input = array(
array('sn' => 1, 'name' => 'Clement', 'upper' => 0),
array('sn' => 2, 'name' => 'Jean', 'upper' => 1),
array('sn' => 3, 'name' => 'Annie', 'upper' => 1),
array('sn' => 4, 'name' => 'Yuan', 'upper' => 2),
array('sn' => 5, 'name' => 'Mei', 'upper' => 2),
array('sn' => 6, 'name' => 'Blue', 'upper' => 3),
array('sn' => 7, 'name' => 'Yang', 'upper' => 5),
array('sn' => 8, 'name' => 'Lorinda', 'upper' => 0),
);
using references you can build a tree with the following loop:
$map = array();
foreach ($input as $node) {
// init self
if (!array_key_exists($node['sn'], $map)) {
$map[$node['sn']] = array('self' => $node['name']);
}
else {
$map[$node['sn']]['self'] = $node['name'];
}
// init parent
if (!array_key_exists($node['upper'], $map)) {
$map[$node['upper']] = array();
}
// add to parent
$map[$node['upper']][$node['sn']] = & $map[$node['sn']];
}
print_r($map[0]);
demo: http://3v4l.org/vuVPu

Answer 2

Assuming the data is like this
$data = array(
array(1, 'Clement', 0),
array(2, 'Jean ', 1),
array(3, 'Annie ', 1),
array(4, 'Yuan ', 2),
array(5, 'Mei ', 2),
array(6, 'Blue ', 3),
array(7, 'Yang ', 5),
array(8, 'Lorinda', 0),
);
this recursive function might work:
function tree($data, $node) {
foreach($data as $e)
if($e[2] == $node[0])
$node['children'] []= tree($data, $e);
return $node;
}
Use it like this:
$tree = tree($data, array(0));
print_r($tree);

Answer 3

using a reference map
$input = array(
array('sn' => 1, 'name' => 'Clement', 'upper' => 0),
array('sn' => 2, 'name' => 'Jean', 'upper' => 1),
array('sn' => 3, 'name' => 'Annie', 'upper' => 1),
array('sn' => 4, 'name' => 'Yuan', 'upper' => 2),
array('sn' => 5, 'name' => 'Mei', 'upper' => 2),
array('sn' => 6, 'name' => 'Blue', 'upper' => 3),
array('sn' => 7, 'name' => 'Yang', 'upper' => 5),
array('sn' => 8, 'name' => 'Lorinda', 'upper' => 0),
);
$map = []; // map a reference by id for each item
foreach ($input as &$inp) {
$map[$inp['sn']] = &$inp;
}
foreach ($map as &$_inp) { // assign each item to its parent, with help of the map
if ($_inp['upper']) {
$map[$_inp['upper']]['children'] = &$map[$_inp['upper']]['children'] ?? [];
$map[$_inp['upper']]['children'][] = &$_inp;
}
}
$result = array_filter($map, fn($item) => !$item['upper']);
print_r($result);```