$inputArray = Array (
    'p.c.f' => 1,
    'p.c.f2' => 2,
    'p2.c.n' => 'test',
    'p2.c2.n' => 'test',
    'p2.c2.p' => 10,
    'p3.c3.p' => 10
);

function transformArray($inputArray){
    $tmp = array();
    $result = array();
    $explode = '';
    $i=0;
    foreach($inputArray as $key => $value){
        $explode = explode('.', $key);
        $tmp[$i][$explode[0]] = array($explode[1] => array($explode[2] => $value));
        $result = array_merge_recursive($result, $tmp[$i]);
        $i++;
    }
    return $result;
}

$result = transformArray($inputArray);
"<pre>".print_r($result)."</pre>";