Sort each subset in a 3-level array by four column values

I have the following multi-dimensional array that I want to sort.

I want to sort the innermost arrays by total_points, then tiebraker1, 2 and 3.

Example:

[
    1 => [
        1 => [
            'userid' => 17,
            'total_points' => 16,
            'tiebraker1' => 1,
            'tiebraker2' => 2,
            'tiebraker3' => 1
        ],
        2 => [
            'userid' => 29,
            'total_points' => 16,
            'tiebraker1' => 1,
            'tiebraker2' => 2,
            'tiebraker3' => 9
        ]
    ],
    2 => [
        1 => [
            'userid' => 26,
            'total_points' => 26,
            'tiebraker1' => 2,
            'tiebraker2' => 2,
            'tiebraker3' => 4
        ],
        2 => [
            'userid' => 17,
            'total_points' => 26,
            'tiebraker1' => 3,
            'tiebraker2' => 2,
            'tiebraker3' => 4
       ]
    ]
]

Desired result:

[
    1 => [
        1 => [
            'userid' => 29,
            'total_points' => 16,
            'tiebraker1' => 1,
            'tiebraker2' => 2,
            'tiebraker3' => 9
        ],
        2 => [
            'userid' => 17,
            'total_points' => 16,
            'tiebraker1' => 1,
            'tiebraker2' => 2,
            'tiebraker3' => 1
        ]
    ],
    2 => [
        1 => [
            'userid' => 17,
            'total_points' => 26,
            'tiebraker1' => 3,
            'tiebraker2' => 2,
            'tiebraker3' => 4
        ],
        2 => [
            'userid' => 26,
            'total_points' => 26,
            'tiebraker1' => 2,
            'tiebraker2' => 2,
            'tiebraker3' => 4
       ]
    ]
]

I tried using array_multisort but I can't configure it correctly.

To use array_multisort you would need a different structure for your data. Specifically you would need to group by "score type" (or expressed mathematically, transpose the array). E.g. like this using your first example:

array(5) {
    // $userid
    [0] => array(2) {
        [0] => 17
        [1] => 29
    }

    // $total_points
    [1] => array(2) {
        [0] => 16
        [1] => 16
    }

    // $tiebreaker1
    [2] => array(4) {
        [0] => 1
        [1] => 1
    }

    // $tiebreaker2
    [3] => array(2) {
        [0] => 2
        [1] => 2
    }

    // $tiebreaker3
    [4] => array(2) {
        [0] => 1
        [1] => 9
    }
}

Then you could use array_multisort() as follows:

array_multisort($ar[1], SORT_DESC, SORT_NUMERIC,
                $ar[2], SORT_DESC, SORT_NUMERIC,
                $ar[3], SORT_DESC, SORT_NUMERIC,
                $ar[4], SORT_DESC, SORT_NUMERIC,
                $ar[0], SORT_ASC, SORT_NUMERIC);

If you cannot change the structure of the array, you could use usort() instead and define the comparision criteria manually.

function cmp($a, $b)
{
    if ($a['total_points'] != $b['total_points']) {
        return ($a['total_points'] > $b['total_points']) ? -1 : 1;
    } elseif ($a['tiebreaker1'] != $b['tiebreaker1']) {
        return ($a['tiebreaker1'] > $b['tiebreaker1']) ? -1 : 1;   
    } elseif ($a['tiebreaker2'] != $b['tiebreaker2']) {
        return ($a['tiebraker2'] > $b['tiebreaker2']) ? -1 : 1;   
    } elseif ($a['tiebreaker3'] != $b['tiebreaker3']) {
        return ($a['tiebreaker3'] > $b['tiebreaker3']) ? -1 : 1;   
    } else {
        return 0;
    }
}

usort($array, "cmp");

Disclaimer: I do not claim that my implementation of cmp is the most elegant one. But it should do the trick. :)