Fastest way to process this array using PHP

I am looking to go from:

array($ID => array (name => $name, created => $timestamp))

e.g

[5632][name] = martin
[5开发者_开发百科632][created] = 131232342
[6742][name] = paul
[6742][created] = 131232312
[6321][name] = peter
[6321][created] = 131232311

to an array of ids ordered by creation like

[0] = 6321
[1] = 6742
[2] = 5632

What is the fastest way to achieve such in PHP?

function sort_by_date($a, $b)
{
  if ($a['created'] == $b['created']) return 0;
  return ($a['created'] < $b['created']) ? -1 : 1;
}

$array = array(...);
uasort($array, "sort_by_date");
$ids = array_keys($array);

uasort lets you sort an array by using a custom function while maintaining keys. array_keys returns an array containing the keys of another array.

Why go through the effort of sorting the entire array of arrays, when you just want the ids?

$times = array();
foreach ($array as $key => $item) {
    $times[$key] = $item['created'];
}
asort($times);
$ids = array_keys($times);

$new_array = krsort(array_keys($your_array));