如何用PHP中的键对数组进行排序？

Question

Array(
    ["car"] => Array(
                     [12/11/1989] => (...)
                     [6/14/2011] => (...)
                     [5/2/2012] => (...)
               )
    ["sled"] => Array(
                     [1/15/2001] => (...)
                     [4/14/2004] => (...)
                     [5/23/2005] => (...)
               )
    ["boat"] => Array(
                     [12/1/1999] => (...)
                     [6/14/2000] => (...)
                     [8/23/2000] => (...)
               )
)

Given the above array structure, I am trying to sort the keys ["boat"], ["sled"], ["car"] by the first date key in their respective sub-arrays. So the correct key order would now be car, boat, sled. Is there an elegant or easy way to do this with PHP?

Answer 1

Use uasort() to sort the array with a user-supplied comparison function, keeping the keys of the associative array.

function compare_first_key_date($a, $b) {
    $a_keys = array_keys($a);
    $a_date = strtotime($a_keys[0]);
    $b_keys = array_keys($b);
    $b_date = strtotime($b_keys[0]);
    return $a_date - $b_date;
}
uasort($array, 'compare_first_key_date');