mongodb aggregate with more than one project operation

Asked Apr 26 '18 at 07:59

Active Apr 26 '18 at 07:59

Viewed 37 times

I am doing a time series application (each document has a timestamp and a value) and need to aggregate values by grouping into time slots (intervals). To make the time slot, the timestamp is divided and then floored. For example a slot of 1-minute:

db.collection.aggregate([
  {$project: {value:1, "timestamp": {$subtract: ["$time", new Date('1970-01-01')]}} },
  {$project: {value:1, "time2": {$divide, ["$timestamp",60000]}}},
  {$project: {value:1, "timeslot": {$floor: "$time2"}}},
  {$group: {_id: "$timeslot", avg: {$avg, "$value"}}}
])

This did the job, but very clumsy: 3 $project in sequence, value:1 repeated each time. Is there a way to combine the $subtract, $divide, $floor... ?

Moreover, are there convenience methods in com.mongodb.client.model.Projections to do this? I am using Java mongodb-driver 3.6.2.

asked Apr 26 '18 at 07:59

cpliu338

What do you actually think that math is doing? Are you actually trying to get a time interval? Because simply dividing by 60,000 would not be correct if that is your intent. – Neil Lunn Apr 26 '18 at 08:05
Don't worry, I just read that you said 1 minute interval. Been answered already. – Neil Lunn Apr 26 '18 at 08:07
Thanks that worked. Upvoted answer to that question. – cpliu338 Apr 26 '18 at 23:15

mongodb aggregate with more than one project operation

0 Answers0