rsort.php

<?php
$a = [
    1 => ['' => 'Foobar'],
    2 => ['Bar'],
    3 => ['Foo']
];

$assertedOutput = [
    0 => ['Foo'],
    1 => ['Bar'],
    2 => ['' => 'Foobar']
];

rsort($a);
print_r($a);

?>

/****** PHP 5.5.9-1ubuntu4.21  *******/
Array
(
    [0] => Array
        (
            [0] => Foo
        )

    [1] => Array
        (
            [0] => Bar
        )

    [2] => Array
        (
            [] => Foobar
        )

)


/****** PHP 7.0.15-0ubuntu0.16.04.4  *******/
Array
(
    [0] => Array
        (
            [] => Foobar
        )

    [1] => Array
        (
            [0] => Foo
        )

    [2] => Array
        (
            [0] => Bar
        )

)