Aggregation framework for MongoDB - mongodb

Question

I have following schema:
Customer ID
Location Name
Time of Visit
The above stores the information of all customer's visit at various locations.
I would like to know if there's a way to write an aggregate query in MongoDB, so that it gives the Total Visitor information by different sections of the day, per day per location.
Sections of the day:
EDIT:
12 am - 8 am
8 am - 11 am
11 am - 1 pm
1 pm - 4 pm
4 pm - 8 pm
8 pm - 12 pm
If a customer visits a location on the same day and same section of the day more than once, it should be counted just once. However, if that customer visits a location on the same day but for different sections of the day, it should be counted exactly once for each of the section of the day he has appeared in.
Example:
Customer 1 visits store A on day 1 at 9:30 AM
Customer 1 visits store A on day 1 at 10:30 PM
Customer 1 visits store B on day 2 at 9:30 AM
Customer 1 visits store B on day 2 at 11:30 AM
Customer 1 visits store B on day 2 at 2:45 PM
Customer 2 visits store A on day 1 at 9:45 AM
Customer 2 visits store B on day 1 at 11:00 AM
Customer 2 visits store B on day 2 at 9:45 AM
Final output of repeat visits:
Store B, Day 1, Section (00:00 - 08:00) : 0 Visitors
Store B, Day 1, Section (08:00 - 16:00) : 2 Visitors
Store B, Day 1, Section (16:00 - 24:00) : 1 Visitors
Store B, Day 2, Section (00:00 - 08:00) : 0 Visitors
Store B, Day 2, Section (08:00 - 16:00) : 2 Visitors
Store B, Day 2, Section (16:00 - 24:00) : 0 Visitors
Is there any way the above kind of query could be done using aggregation framework for MongoDB?

Answer 1

Yes, this can be done quite simply. It's very similar to the query that I describe in the answer to your previous question, but rather than aggregating by day, you need to aggregate by day-hour-combinations.
To start with, rather than doing a group you will need to project a new part of date where you need to transform your "Time of Visit" field to the appropriate hour form. Let's look at one way to do it:
{$project : { newDate: {
y:{$year:"$tov"}, m:{$month:"$tov"}, d:{$dayOfMonth:"$tov"},
h: { $subtract :
[ { $hour : "$tov" },
{ $mod : [ { $hour : "$tov" }, 8 ] }
]
}
},
customerId:1, locationId:1
}
}
As you can see this generates year, month, day and hour but the hour is truncated to mod 8 (so you get 0, 8(am), or 16 aka 4pm.
Next we can do the same steps we did before, but now we are aggregating to a different level of time granularity.
There are other ways of achieving the same thing, you can see some examples of date manipulation on my blog.