Get all values from specific key in a multidimensional array, similar to array_columns

array-value-recursive.php

<?php

/**
 * Get all values from specific key in a multidimensional array
 *
 * @param string $key key(s) of value you wish to extract
 * @param array  $arr where you want
 *
 * @return null|string|array
 */
function array_value_recursive($key, array $arr)
{
    $val = array();
    array_walk_recursive($arr, function ($v, $k) use ($key, &$val) {
        if ($k == $key) array_push($val, $v);
    });
    return count($val) > 1 ? $val : array_pop($val);
}

one refactor

    /**
     * This function extracts all values from a specific key in a multidimensional array, 
     * or all values if key is not provided. It can also remove 
     * duplicates depending on the "uniqueVal" parameter.
     */
    function array_value_recursive(array $arr, ?string $key = null, bool $unique = true): array
    {
        array_walk_recursive($arr, function ($v, $k) use ($key, &$val) {
           if (is_null($key) || ($key && $k == $key)) {
                $val[] = $v;
            }
        });

        return $unique ? array_unique($val ?? []) : $val ?? [];
    }