From http://stackoverflow.com/questions/1597736/how-to-sort-an-array-of-associative-arrays-by-value-of-a-given-key-in-php

sort_multidim_assoc_by_nested_value.php

<?php
// sort 'inventory' array by 2nd level value 'price'

$price = array();
foreach ($inventory as $key => $row)
{
    $price[$key] = $row['price'];
}
array_multisort($price, SORT_DESC, $inventory);

?>