How to Sort a Multi-dimensional Array by Value?

function sortByOrder($a, $b) {
    if ($a['order'] > $b['order']) {
        return 1;
    } elseif ($a['order'] < $b['order']) {
        return -1;
    }
    return 0;
}

usort($myArray, 'sortByOrder');

Starting in PHP 5.3, you can use an anonymous function:

usort($myArray, function($a, $b) {
    if ($a['order'] > $b['order']) {
        return 1;
    } elseif ($a['order'] < $b['order']) {
        return -1;
    }
    return 0;
});

With PHP 7 you can use the spaceship operator:

usort($myArray, function($a, $b) {
    return $a['order'] <=> $b['order'];
});

Finally, in PHP 7.4 you can clean up a bit with an arrow function:

usort($myArray, fn($a, $b) => $a['order'] <=> $b['order']);

To extend this to multi-dimensional sorting, reference the second/third sorting elements if the first is zero - best explained below. You can also use this for sorting on sub-elements.

usort($myArray, function($a, $b) {
    $retval = $a['order'] <=> $b['order'];
    if ($retval == 0) {
        $retval = $a['suborder'] <=> $b['suborder'];
        if ($retval == 0) {
            $retval = $a['details']['subsuborder'] <=> $b['details']['subsuborder'];
        }
    }
    return $retval;
});

If you need to retain key associations, use uasort() - see comparison of array sorting functions in the manual.