Here we will learn how we can sort two dimensional array:-

lets take an example :-

<?php
$activities = array (
    '1' => array(
        'id' => 1,
        'time' => "2015-10-22 14:20:00"
    ),
    '2' => array(
        'id' => 2,
        'time' => "2015-09-15 22:20:00"
    ),
    '3' => array(
        'id' => 1,
        'time' => "2015-01-25 22:20:00"
    )
);
    echo 'Before Sorting <br>';
    echo '<pre>';
    print_r($activities);
    echo '</pre>';
?>

run this code in the browser.

So now above array we will sort by time key,

<?php 
function multid_sort($arr, $index) {
    $b = array();
    $c = array();
    foreach ($arr as $key => $value) {
        $b[$key] = $value[$index];
    }
    asort($b);
    foreach ($b as $key => $value) {
        $c[] = $arr[$key];
    }
    return $c;
}
$sorted_act = multid_sort($activities, 'time');

echo 'After Sorting <br>';
echo '<pre>';
print_r($sorted_act);
echo '</pre>';
?>

Now run the above code in browser, you will see the output below :-

Before Sorting 
Array
(
    [1] => Array
        (
            [id] => 1
            [time] => 2015-10-22 14:20:00
        )

    [2] => Array
        (
            [id] => 2
            [time] => 2015-09-15 22:20:00
        )

    [3] => Array
        (
            [id] => 1
            [time] => 2015-01-25 22:20:00
        )

)
After Sorting 
Array
(
    [0] => Array
        (
            [id] => 1
            [time] => 2015-01-25 22:20:00
        )

    [1] => Array
        (
            [id] => 2
            [time] => 2015-09-15 22:20:00
        )

    [2] => Array
        (
            [id] => 1
            [time] => 2015-10-22 14:20:00
        )

)

Enjoy the code :)