按日期键按子数组排序PHP数组

Question

I know this question has been asked a hundred times, and I've gone through multiple answers and am not getting the correct results.

I am trying to order the following row by date, oldest first:

Array(
[0] => Array
    (
        [0] => '3173'
        [1] => 'Contact - 12-6-14 Outstanding invoice'
        [2] => '16/06/2014'
        [3] => '204'
    )

[1] => Array
    (
        [0] => '3167'
        [1] => 'Contact - Outstanding invoice'
        [2] => '13/06/2014'
        [3] => '207'
    )

[2] => Array
    (
        [0] => '3497'
        [1] => 'New Site - Keri Keri'
        [2] => '25/11/2014'
        [3] => '43'
    )

[3] => Array
    (
        [0] => '2023'
        [1] => 'Analysis'
        [2] => '17/06/2014'
        [3] => '355'
    )

[4] => Array
    (
        [0] => '2641'
        [1] => 'PSS'
        [2] => '20/02/2014'
        [3] => '321'
    )

)

I have tried things such as the below with no luck.

function cmp($a, $b){
      return $b[2] - $a[2];
   } 

usort($urgent_array, "cmp");

Any help on this one would be really appreciated :)

Answer 1

First, you want to compare, not subtract:

function cmp($a, $b) {
    if ($a[2] == $b[2])
        return 0;
    return ($a[2] > $b[2]) ? 1 : -1;
} 

usort($urgent_array, "cmp");

Then, date ordering works best if you use the Y-m-d format:

2014-06-13 etc.