根据日期和其他字段聚合来自Mongo集合的数据，并计数

I keep a collection of events, counting by day. If the event occurs once then it's a 'hit' (billState), this is per location and material class. I am having a hard time getting the data back out that I need, I have tried several examples found here at SO, and many in the Mongo Docs.. usually ending up with only parts of what I need to get out.I keep a collection of events, counting by day.