Cookies help us deliver our services. By using our services, you agree to our use of cookies. More information

Sum and Count

From NoSQLZoo
Revision as of 15:05, 27 July 2015 by 40166222 (talk | contribs)
Jump to: navigation, search
#ENCODING
import io
import sys
sys.stdout = io.TextIOWrapper(sys.stdout.buffer, encoding='utf-16')
#MONGO
from pymongo import MongoClient
client = MongoClient()
client.progzoo.authenticate('scott','tiger')
db = client['progzoo']
#PRETTY
import pprint
pp = pprint.PrettyPrinter(indent=4)
#CODE
from bson.code import Code

There are many ways to do this in MongoDB.

count() is a cursor method that takes a query and returns a number equal to the amount of documents that matched the query.
$sum is an aggregation operator availible in the $group stage, that can be used to both sum values and count the number of documents.
mapReduce can produce a sum or a count during the results stage.

.count()
print(db.world.count({"continent":"Africa"}))
$sum

pp.pprint(list(

   db.world.aggregate([
       {"$group":{
           "_id":"$continent",
           "sum of population":{"$sum":"$population"},
           "count of countries":{"$sum":1}
       }}
   ])

))

.count()

print(db.world.count("continent":"Africa"))