So, the idea of groups would be to allow some privacy. from the global system - and make it easier to find/follow posts from groups you care about.
It needs to support quite a few different things
The data model could look like:
-list of people
-hidden (can non-members see posts?)
types should include:
-public - anyone can join
-invite - anyone can invite
-admin - admins can invite
-democratic - people must be voted in
-automatic?, spreads to any friend , perhaps just one group like this?
full sum: 4
full vote count: 5
direct sum: 0.8
direct vote count: 1