Sort array by object property in PHP?

Question

If I have an object as such:

class Person {
  var $age;
  function __construct($age) {
    $this->age = $age;
  }
}

and I have any array

Answer 1

Here’s a stable Radix Sort implementation for values 0...256:

function radixsort(&$a)
{
    $n = count($a);
    $partition = array();
    for ($slot = 0; $slot < 256; ++$slot) {
        $partition[] = array();
    }
    for ($i = 0; $i < $n; ++$i) {
        $partition[$a[$i]->age & 0xFF][] = &$a[$i];
    } 
    $i = 0;
    for ($slot = 0; $slot < 256; ++$slot) {
        for ($j = 0, $n = count($partition[$slot]); $j < $n; ++$j) {
            $a[$i++] = &$partition[$slot][$j];
        }
    }
}

This costs only O(n) since Radix Sort is a non-comparing sorting algorithm.