Difference between revisions of "AGGREGATE world"

Revision as of 12:17, 17 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)

Country Profile

For these questions you should use aggregate([]) on the collection world

Give the name and the per capita GDP for those countries with a population of at least 200 million.

per capita GDP is the GDP divided by the population.

pp.pprint(list(
    db.world.aggregate([
        {"$match":{
            "population":{"$gte":250000000}
        }},
        {"$project":{
            "_id":0,
            "name":1,
            "per capita GDP": {"$divide": ["$gdp",1000000]}
        }}
    ])
))

pp.pprint(list(db.world.aggregate([{"$match":{"population":{"$gte":200000000}}},{"$project":{"_id":0,"name":1,"per capita GDP": {"$divide": ["$gdp","$population"]}}}])))

Give the name and the population density of all countries.

population density is the population divided by the area

Use a $match. {"area":{"$ne":0}}


pp.pprint(list(
    db.world.aggregate([
        {"$project":{
            "_id":0,
            "name":1,
            "per capita GDP": {"$divide": [10000,"$area"]}
        }}
    ])
))


pp.pprint(list(

   db.world.aggregate([
       {"$match":{
           "area":{"$ne":0}
       }},
       {"$project":{
           "_id":0,
           "name":1,
           "per capita GDP": {"$divide": [10000,"$area"]}
       }}
   ])

))

@@ Line 44: / Line 44: @@
 <div class="hint" title="How to calculate population density">
 population density is the population divided by the area
+</div>
+<div class="hint" title="Division by 0 error?">
+<code> Use a <code>$match</code>. <code>{"area":{"$ne":0}}</code>
 </div>
 <pre class=def>
@@ Line 56: / Line 59: @@
 ))
 </pre>
-<div class=ans>pp.pprint(list(db.world.aggregate([{"$match":{"population":{"$gte":200000000}}},{"$project":{"_id":0,"name":1,"per capita GDP": {"$divide": ["$gdp","$population"]}}}])))
+<div class=ans>
+pp.pprint(list(
+    db.world.aggregate([
+        {"$match":{
+            "area":{"$ne":0}
+        }},
+        {"$project":{
+            "_id":0,
+            "name":1,
+            "per capita GDP": {"$divide": [10000,"$area"]}
+        }}
+    ])
+))
 </div>
 </div>