Simplify a nested array into a single level array [duplicate]

Answer 1

I have searched all similar questions and it seems there is no way without a recursion that would keep the keys order intact.

So I just went with classic recursion:

function getArrayKeysRecursive(array $theArray)
{
    $aArrayKeys = array();
    foreach ($theArray as $k=>$v) {
        if (is_array($v)) {
            $aArrayKeys = array_merge($aArrayKeys, array($k), getArrayKeysRecursive($v));
        } else {
            $aArrayKeys = array_merge($aArrayKeys, array($k));
        }
    }
    return $aArrayKeys;
}