无法在codeigniter中创建多维数组

$data = array(
    'user' => array(
        'name' => 'John',
        'email' => 'john@example.com',
        'address' => array(
            'street' => '123 Main St',
            'city' => 'New York',
            'state' => 'NY'
        )
    ),
    'product' => array(
        'name' => 'iPhone',
        'price' => 999
    )
);

// 获取用户的姓名
$name = $data['user']['name'];

// 修改产品的价格
$data['product']['price'] = 899;

// 添加新的属性
$data['user']['age'] = 25;

// 删除地址信息
unset($data['user']['address']);