Sort array based on different columns - php

Question

I created an array based on a mysql table
Array (
[0] => Array ( [id] => 1 [parent_ID] => 0 )
[1] => Array ( [id] => 2 [parent_ID] => 0 )
[2] => Array ( [id] => 3 [parent_ID] => 2 )
[3] => Array ( [id] => 4 [parent_ID] => 2 )
[4] => Array ( [id] => 5 [parent_ID] => 2 )
[5] => Array ( [id] => 6 [parent_ID] => 1 )
[6] => Array ( [id] => 7 [parent_ID] => 1 )
[7] => Array ( [id] => 8 [parent_ID] => 1 )
[8] => Array ( [id] => 9 [parent_ID] => 1 )
I want to create a new array, where the order of the parent_ID is based on the ID. If the parent_ID from an array is “1”, than it needs to be placed directly after the array that has ID “1”. The output of the new array needs to be like this:
Array (
[0] => Array ( [id] => 1 [parent_ID] => 0 )
[1] => Array ( [id] => 6 [parent_ID] => 1 )
[2] => Array ( [id] => 7 [parent_ID] => 1 )
[3] => Array ( [id] => 8 [parent_ID] => 1 )
[4] => Array ( [id] => 9 [parent_ID] => 1 )
[5] => Array ( [id] => 2 [parent_ID] => 0 )
[6] => Array ( [id] => 3 [parent_ID] => 2 )
[7] => Array ( [id] => 4 [parent_ID] => 2 )
[8] => Array ( [id] => 5 [parent_ID] => 2 )
I tried to order my array by using the usort function, but that will only order the parent_ID or the ID column. Is it possible with PHP to sort an array like the example?

Answer 1

As said in my comment to the question your proposed result is bogus...
But here is some simple algorithm constructing such output:
<?php
$input = [
['id' => 1, 'parent_ID' => 0],
['id' => 2, 'parent_ID' => 0],
['id' => 3, 'parent_ID' => 2],
['id' => 4, 'parent_ID' => 2],
['id' => 5, 'parent_ID' => 2],
['id' => 6, 'parent_ID' => 1],
['id' => 7, 'parent_ID' => 1],
['id' => 8, 'parent_ID' => 1],
['id' => 9, 'parent_ID' => 1]
];
$data = [];
$output = [];
array_walk ($input, function($entry) use (&$data) {
$data[$entry['parent_ID']][] = $entry;
});
array_walk ($data[0], function($entry) use ($data, &$output) {
$output[] = $entry;
foreach ($data[$entry['id']] as $child) {
$output[] = $child;
}
});
print_r($output);
The output of executing that obviously is:
Array
(
[0] => Array
(
[id] => 1
[parent_ID] => 0
)
[1] => Array
(
[id] => 6
[parent_ID] => 1
)
[2] => Array
(
[id] => 7
[parent_ID] => 1
)
[3] => Array
(
[id] => 8
[parent_ID] => 1
)
[4] => Array
(
[id] => 9
[parent_ID] => 1
)
[5] => Array
(
[id] => 2
[parent_ID] => 0
)
[6] => Array
(
[id] => 3
[parent_ID] => 2
)
[7] => Array
(
[id] => 4
[parent_ID] => 2
)
[8] => Array
(
[id] => 5
[parent_ID] => 2
)
)
However I would like to make some comments to your situation:
you really should not store a value of 0 for the first elements. They do not have a parent, if I get your situation right, so that value should actually be null, not 0.
you should try to order your data right in the SQL query
you should rethink the overall approach since apparently you have huge issues sorting your data with the given data model. That typically is a sign of a modelling approach that should be reworked.