How to find the median of deepest subarrays of multidimensional array?

Question

I have a four-level multidimensional array. I need to sort in ascending order (ASC) the numeric "leaves" in order to calculate the median of the values.

I tried array_walk_recursive(), array_multisort(), usort(), etc. but was unable to find a working solution.

Here's a schematic of the array:

(
    [2017-05-01] => Array
        (
            [DC] => Array
                (
                    [IT] => Array
                        (
                            [0] => 90
                            [1] => 0
                        )    
                    [DE] => Array
                        (
                            [0] => 18
                            [1] => 315
                            [2] => 40
                            [3] => 
                            [4] => 69
                        )    
                    [Other] => Array
                        (
                            [0] => 107
                            [1] => 46
                            [2] => 
                            [3] => 
                            [4] => 27
                            [5] => 22
                        )    
                )
        )
)

Answer 1

This will output the deepest subarrays' median values using the input array's structure.

I'm including hard-casting of median values (one or both in a subset) as integers in the event that the value(s) are empty strings. I'll also assume that you will want 0 as the output if a subset is empty.

Create a new array in a functional style: Demo

var_export(
    array_map(
        fn($dateSet) => array_map(
            fn($dcSet) => array_map(
                function ($set) {
                    if (!$set) {
                        return 0;
                    }
                    sort($set);
                    $count = count($set);
                    $mid = intdiv($count, 2);
                    if ($count & 1) {
                        return $set[$mid];
                    }
                    return ((int)$set[$mid - 1] + (int)$set[$mid]) / 2;
                },
                $dcSet
            ),
            $dateSet
        ),
        $array
    )
);

Or modify the input array by reference in a classic loop. Demo

foreach ($array as &$dateSet) {
    foreach ($dateSet as &$dcSet) {
        foreach ($dcSet as &$set) {
            if (!$set) {
                $set = 0;
                continue;
            }
            sort($set);
            $count = count($set);
            $mid = intdiv($count, 2);
            if ($count & 1) {
                $set = $set[$mid];
                continue;
            }
            $set = ((int)$set[$mid - 1] + (int)$set[$mid]) / 2;
        }
    }
}
var_export($array);

Or modify the input array by reference with array_walk(). Demo

array_walk(
    $array,
    fn(&$dateSet) => array_walk(
        $dateSet,
        fn(&$dcSet) => array_walk(
            $dcSet,
            function (&$set) {
                if (!$set) {
                    $set = 0;
                    return;
                }
                sort($set);
                $count = count($set);
                $mid = intdiv($count, 2);
                if ($count & 1) {
                    $set = $set[$mid];
                    return;
                }
                $set = ((int)$set[$mid - 1] + (int)$set[$mid]) / 2;
            }
        )
    )
);
var_export($array);

*for the record, $count & 1 is a bitwise comparison that determines if the value is odd without performing arithmetic (and is the most efficient way of performing this check within php).

*also, if you wanted to simply overwrite the values of the input array, you could modify by reference by writing & before $lv1, $lv2, and $lv3 in the foreach declarations then save the median value to $lv3. Demo The benefit in doing so removes key declarations and making your code more brief.