Sort each subarray of a 2d array by delimited string values

Original array:

$resolutions =  array (
    "Desktop monitor" => array (
        //Standard 4:3
        "800x600" => "800x600",
        "1024x768" => "1024x768",
        "1600x1200" => "1600x1200",
        //Wide 16:10
        "960x600" => "960x600",
        "1280x800" => "1280x800",
        "1440x900" => "1440x900",
        "1680x1050" => "1680x1050",
        "1920x1200" => "1920x1200",
    ),
    "Apple" => array (
        "DeviceX" => "2048x1536",
        "DeviceY" => "1024x768",
    ),
);

Wanted array:

$resolutions =  array (
    "Desktop monitor" => array (
        "800x600" => "800x600",//Standard 4:3
        "960x600" => "960x600",//Wide 16:10
        "1024x768" => "1024x768",//Standard 4:3
        "1280x800" => "1280x800",//Wide 16:10
        "1440x900" => "1440x900",//Wide 16:10
        "1600x1200" => "1600x1200",//Standard 4:3
        "1680x1050" => "1680x1050",//Wide 16:10
        "1920x1200" => "1920x1200",//Wide 16:10
    ),
    "Apple" => array (
        "DeviceY" => "1024x768",
        "DeviceX" => "2048x1536",
    ),
);

What I have tried:

foreach ($resolutions as $screen => $resolution) { 
    foreach($resolution as $key => $val) {
        $newarray[$key] = $row[$val];
    }
    array_multisort($newarray, SORT_DESC, $resolution);
}

I thought that I'm half way to end, but the code above gave me some non sense (for me), ie: first goes resolution 1024x768, then 1280x800, followed by 1440x900 and in the end is 800x600.

The problem is that you are sorting alphabetically. You will need to calculate the size of each resolution to sort them correctly. This will require writing a custom comparison function that calculate the resolution sizes and compare them.

foreach ($resolutions as &$resolution)
    uasort($resolution, function ($a, $b) { return array_product(explode('x', $a)) - array_product(explode('x', $b)); });