Remove all elements of an array with non-numeric keys

Using a foreach loop would be appropriate in this case:

foreach ($arr as $key => $value) {
    if (!is_int($key)) {
        unset($arr[$key]);
    }
}

It can be done without writing a loop in one (long) line:

$a = array_intersect_key($a, array_flip(array_filter(array_keys($a), 'is_numeric')));

What it does:

• Since array_filter works with values, array_keys first creates a new array with the keys as values (ignoring the original values).
• These are then filtered by the is_numeric function.
• The result is then flipped back so the keys are keys once again.
• Finally, array_intersect_key only takes the items from the original array having a key in the result of the above (the numeric keys).

Don't ask me about performance though.