使用第二级值对二维数组进行排序

I have a 2 dimensions array and need to sort it according to some of the second dimension values.
I tried using uksort, but it doesn't work:

$arr = array();
$arr[] = array('name'=>'test1', 'age'=>25);
$arr[] = array('name'=>'test2', 'age'=>22);
$arr[] = array('name'=>'test3', 'age'=>23);
$arr[] = array('name'=>'test4', 'age'=>29);
uksort($arr, "cmp");
print_r($arr);

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

Can anyone spot what am I doing wrong?

I think you are looking for uasort().

uksort() will order your array by keys, but you want to sort the arrays by their value.

uksort

Sort an array by keys using a user-defined comparison function

Sorting array by keys means that you take value of a key (in your case it is the same string age for all subarrays). And you sort by value.

So usort is enough - fiddle.