How to Mine Data from a Facebook Group?

I am using RFacebook package to do data mining. For example, to get the facebook page (http://ift.tt/MKrQcH) then we do

fb_page <- getPage(page="facebook", token=fb_oauth)

In my case is it is a private group and the URL is something like this http://ift.tt/1FtSIr7. So how do I get the page info for a group? I tried the following but got the following error.

Error in callAPI(url = url, token = token) : Unknown path components: /posts

  my_page <- getPage(page="group/222568978569", token=my_oauth)

Any suggestions would be greatly appreciated.

Thank you