Sorting a php array of arrays by custom order

Question

I have an array of arrays:

Array ( 
    [0] => Array (
        [id] = 7867867,
        [title] = 'Some Title'),
    [1] => Array (
        [id] = 3452342,
        [title] = 'Some Title'),
    [2] => Array (
        [id] = 1231233,
        [title] = 'Some Title'),
    [3] => Array (
        [id] = 5867867,
        [title] = 'Some Title')
)

The need to go in a specific order:

1. 3452342
2. 5867867
3. 7867867
4. 1231233

How would I go about doing that? I have sorted arrays before, and read plenty of other posts about it, but they are always comparison based (i.e. valueA < valueB).

Help is appreciated.

Answer 1

You can use usort() to dictate precisely how the array is to be sorted. In this case, the $order array can be used within the comparison function.

The example below uses a closure to make life easier.

$order = array(3452342, 5867867, 7867867, 1231233);
$array = array(
    array('id' => 7867867, 'title' => 'Some Title'),
    array('id' => 3452342, 'title' => 'Some Title'),
    array('id' => 1231233, 'title' => 'Some Title'),
    array('id' => 5867867, 'title' => 'Some Title'),
);

usort($array, function ($a, $b) use ($order) {
    $pos_a = array_search($a['id'], $order);
    $pos_b = array_search($b['id'], $order);
    return $pos_a - $pos_b;
});

var_dump($array);

The key to this working is having the values that are being compared, be the positions of the ids within the $order array.

The comparison function works by finding the positions of the ids of two items to be compared within the $order array. If $a['id'] comes before $b['id'] in the $order array, then the return value of the function will be negative ($a is less so "floats" to the top). If $a['id'] comes after $b['id'] then the function returns a positive number ($a is greater so "sinks" down).

Finally, there is no special reason for using a closure; it's just my go-to way of writing these sorts of throwaway functions quickly. It could equally use a normal, named function.