“as do I”语法对吗?

以下是yahoo上english speaker的回答
Well to be proper it should be as do I but most people don't care to be that proper and say so do I.It's like if you have a picture of you and another friend when you go to label it you would say my friend and I not me and my friend.Hope this helps and good luck!
正式的说法是so do i,但很多人都习惯说as do i,所以口语中as do i也行