Difference between revisions of "Sum and Count"

Revision as of 15:32, 27 July 2015

#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

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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 by using JavaScript.

.count()

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

$sum

pp.pprint(list(

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

))

Array.sum()

temp = db.world.map_reduce(

   map=Code("function(){emit(this.name, this.population)}"),
   reduce=Code("""function(k,v){
                      return Array.sum(v)
                  }
               """),
   out={"inline":1}

)

pp.pprint(temp['results'])

@@ Line 20: / Line 20: @@
 <code>count()</code> is a cursor method that takes a query and returns a number equal to the amount of documents that matched the query.<br/>
 <code>$sum</code> is an aggregation operator availible in the <code>$group</code> stage, that can be used to both sum values and count the number of documents.<br/>
-mapReduce can produce a sum or a count during the results stage.
+mapReduce can produce a sum or a count during the results stage by using JavaScript.
 </div>
 <div class=q data-lang="py3">.count()
@@ Line 40: / Line 40: @@
 </div>
-<div class=q data-lang="py3">.count()
+<div class=q data-lang="py3">Array.sum()
 <div class="def">temp = db.world.map_reduce(
      map=Code("function(){emit(this.name, this.population)}"),