How to count distinct values in a MongoDB?

Question

I would like to count distinct values in a MongoDB which are between certain dates.

Something like the following in SQL:

select distinct(count(iid)) 
from collection
Where date > 2015-04-03 and date < 2015-04-04

I have been running successfully the following query on the MongoDB, however, this returns the total count (not the count of distinct values):

db.m_2015_04.find(
{ "_timestamp" : { "$gte" : ISODate("2015-04-03T00:00:000Z"), "$lt" : ISODate("2015-04-03T23:59:000Z") }})
.count()

unfortunately ,this result with an error.

Adi Rosenfeld
– Adi Rosenfeld

2015-04-06 13:56:55 +00:00
Commented Apr 6, 2015 at 13:56 — Adi Rosenfeld
– Adi Rosenfeld, Commented Apr 6, 2015 at 13:56

nickmilon · Accepted Answer · 2015-04-06 13:46:35Z

3

what about following ?

db.m_2015_04.distinct('iid', { "_timestamp" : { "$gte" : ISODate("2015-04-03T00:00:000Z"), "$lt" : ISODate("2015-04-03T23:59:000Z") }}).length

answered Apr 6, 2015 at 13:46

nickmilon

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1 Comment

nickmilon Over a year ago

just be aware that distinct will not work if the distinct values exceed 16 MBytes. in this case you got to use aggregation framework or a map reduce job.

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