将字典键与数组进行比较，以提取匹配和非匹配数据

I am trying to retrieve Facebook friends list and display the user if he is following another users or not. For that I am using FacebookID's stored on parse backend and when the user clicks on Follow button, I add his FacebookId to the key value "following" in parse. Later I retrieve this following key array and display the user that the currentUser is following or not following.I am trying to retrieve Facebook friends list a