Как перебрать массив и привести к требуемому виду?

Array
(
    [project_id] => 4
    [user_id_1190647361] => 1190647361
    [user_id_1977462916] => 1977462916
    [user_id_169505052] => 169505052
    [user_id_622870866] => 622870866
    [user_id_1436905292] => 1436905292
    [user_id_2720806559] => 2720806559
)

Array
(
    [0] => Array
        (
            [project_id] => 4
            [user_id] => 1190647361
        )
    [1] => Array
        (
            [project_id] => 4
            [user_id] => 1977462916
        )
    [2] => Array
        (
            [project_id] => 4
            [user_id] => 169505052
        )
    [3] => Array
        (
            [project_id] => 4
            [user_id] => 622870866
        )
    [4] => Array
        (
            [project_id] => 4
            [user_id] => 1436905292
        )
    [5] => Array
        (
            [project_id] => 4
            [user_id] => 2720806559
        )
)

$i = 0;
foreach ($post_data as $key => $item)
{
	if ($key === 'project_id')
	{
		$data[$i][$key] = $item;
	} else
	{
		$data[$i]['user_id'] = $item;
	}
	$i++;
}