Sort an array of arrays by a column value in a descending direction

Question

I've got an array of arrays like this :

Array(
    [id1] => Array (
           /* details */
           [unique] => 3
          )
    [id2] => Array (
           /* details */
           [unique] => 5
    [id3] => Array (
           /* details */
           [unique] => 1
    )
)

Question : How could I sort it by the unique field, so that it is converted like the one following?

Array(
    [id2] => Array (
           /* details */
           [unique] => 5
          )
    [id1] => Array (
           /* details */
           [unique] => 3
    [id3] => Array (
           /* details */
           [unique] => 1
    )
)

Answer 1

Classical task for usort function:

<?php
$data = array(
    "id1" => Array (
        "unique" => 3
        ),
    "id2" => Array (
        "unique" => 5),
    "id3" => Array (
        "unique" => 1
        ),
    );

function cmp($a, $b)
// {{{
{
    if ($a["unique"] == $b["unique"]) {
        return 0;
    }
    return ($a["unique"] < $b["unique"]) ? 1 : -1;
}
// }}}

usort($data, "cmp");
var_dump($data);

Prints:

array(3) {
  [0]=>
  array(1) {
    ["unique"]=>
    int(5)
  }
  [1]=>
  array(1) {
    ["unique"]=>
    int(3)
  }
  [2]=>
  array(1) {
    ["unique"]=>
    int(1)
  }
}

http://www.php.net/manual/en/function.usort.php