Trying to mimic hierarchy by sorting array in PHP

Question

I am trying to sort an array the following way in PHP:

array
0 =>    id:1203
        parent_id: 456

1 =>    id:456
        parent_id:1723

2 =>    id:1723
        parent_id:0

to this:

array   
0 =>    id:1723
        parent_id:0

1 =>    id:456
        parent_id:1723

2 =>    id:1203
        parent_id:456

I never sorted an array in PHP before. How would you do it?

Thanks

So if I understand correctly, you are trying to sort it so that the parent_id is the preceding id? How are you determining what should be the initial ID to start cascading from? — WebChemist
– WebChemist, Commented Jan 26, 2011 at 22:51
Sorry for my late reply. But yeah the initial id would be the one that doesn't have a parent id. Picture it as a tree. If an array doesn't have a parent_id then it's the root basically. — Kel
– Kel, Commented Jan 27, 2011 at 14:04

Toto · Accepted Answer · 2011-01-27 16:20:14Z

1

Is this doing what you want ?

$arr = array(
    array('id' => 1203, 'parent_id' =>  456),
    array('id' =>  456, 'parent_id' => 1723),
    array('id' => 1723, 'parent_id' =>    0)
);

function compare($a, $b) {

    if ($a['parent_id'] == 0) return -1;
    if ($b['parent_id'] == 0) return 1;

    if ($a['id'] == $b['parent_id']) return -1;
    if ($b['id'] == $a['parent_id']) return 1;

    return 0;
}

usort($arr, 'compare');

print_r($arr);

output:

Array
(
    [0] => Array
        (
            [id] => 1723
            [parent_id] => 0
        )

    [1] => Array
        (
            [id] => 456
            [parent_id] => 1723
        )

    [2] => Array
        (
            [id] => 1203
            [parent_id] => 456
        )

)

answered Jan 27, 2011 at 16:20

Toto

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Comments

Jose Armesto · Accepted Answer · 2011-01-26 22:54:07Z

0

I dont see whats the criteria you want to use to sort. Anyway, you could use uasort function , in which you pass a custom function as argument, so in that function you can define whatever criteria you want to order your array. That function would receive 2 arguments (the 2 variables to compare), and you could compare both parent_id (or whatever is you want to compare). To learn what your custom function should return, check this out.

By using uasort instead of usort you can keep your array indexes (as you said in your example).

answered Jan 26, 2011 at 22:54

Jose Armesto

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