What potential issues can arise when filtering arrays in PHP, as seen in the provided code example?

When filtering arrays in PHP, potential issues can arise if the filter function returns unexpected results or if the array keys are not preserved. To solve this, it is important to use the array_filter function with the ARRAY_FILTER_USE_BOTH flag to preserve both keys and values in the filtered array.

// Original code filtering array without preserving keys
$numbers = [1, 2, 3, 4, 5];
$filteredNumbers = array_filter($numbers, function($num) {
    return $num % 2 == 0;
});

// Fix: Use array_filter with ARRAY_FILTER_USE_BOTH flag to preserve keys
$numbers = [1, 2, 3, 4, 5];
$filteredNumbers = array_filter($numbers, function($key, $num) {
    return $num % 2 == 0;
}, ARRAY_FILTER_USE_BOTH);