Moving averages with MongoDB's aggregation framework?

Question

If you have 50 years of temperature weather data (daily) (for example) how would you calculate moving averages, using 3-month intervals, for that time period? Can you do tha

Answer 1

I don't believe the aggregation framework can do this for multiple dates in the current version (2.6), or, at least, can't do this without some serious gymnastics. The reason is that the aggregation pipeline processes one document at a time and one document only, so it would be necessary to somehow create a document for each day that contains the previous 3 months worth of relevant information. This would be as a $group stage that would calculate the average, meaning that the prior stage would have produced about 90 copies of each day's record with some distinguishing key that can be used for the $group.

So I don't see a way to do this for more than one date at a time in a single aggregation. I'd be happy to be wrong and have to edit/remove this answer if somebody finds a way to do it, even if it's so complicated it's not practical. A PostgreSQL PARTITION type function would do the job here; maybe that function will be added someday.