Useful array functions.

array_helpers.php

<?php

/**
 * Only get the values for keys which
 * exist in the array.
 * 
 * Example: array_only_keys(['a' => 'b', 'c' => 'd'], ['a']); // returns ['a' => 'b']
 * 
 * @param  Array         $haystack  The array you want values from
 * @param  Array|String  $keys      Array of keys, or a key which you want from the haystack
 * @return Array
 */
function array_only_keys($haystack, $keys)
{
    return array_filter($haystack, function($v, $k) use ($keys) {
            if (!is_array($keys)) return $k == $keys && $v;
            return in_array($k, $keys) && $v;
    }, ARRAY_FILTER_USE_BOTH);
}