View source for FIND from WORLD

<pre class="setup">
#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)
</pre>

==Working with the <code>world</code> collection of countries==
  <p>This tutorial introduces NoSQL using MonogDB and PyMongo under Python3.4. We will be using the <code>find()</code> command and comparison functions on the collection '''world''' which contains details of around 250 countries of the world:</p>
[[FIND examples]] are available.


<div class=q data-lang="py3">
Observe the result of running a simple mongoDB command.
<p class=strong>FIND name, continent, population FROM world</p>
<pre class=def>
pp.pprint(list(
    db.world.find({},{
      "name":1,
      "continent":1,
      "population":1,
      "_id":0
    })
))
</pre>
<div class=ans>
pp.pprint(list(db.world.find({},{"name":1,"continent":1,"population":1,"_id":0})))
</div>
</div>


<div class=q data-lang="py3">
<p class=strong>Show the name for the countries that have a population of at least 200 million. 200 million is 200000000, there are eight zeros.</p>
<pre class=def>
pp.pprint(list(
    db.world.find(
      {"population":{"$gt":200000000}},
      {"name":1, "_id":0}
    )
))
</pre>
<div class=ans>
pp.pprint(list(db.world.find({"population":{"$gt":200000000}},{"name":1, "_id":0})))
</div>
</div>

<div class=q data-lang="py3">
<p class=strong>Give the name and the per capita GDP for those countries with a population of at least 200 million.</p>
[[AGGREGATE examples]] are available.
<div class="hint" title="How to calculate per capita GDP">per capita GDP is the GDP divided by the population GDP/population</div>
<pre class=def>
pp.pprint(list(
    db.world.aggregate([
        {"$match":{"population":{"$gt":200000000}}},
        {"$project":{"name":1, "gdp/population":{"$divide":["$gdp","$population"]}, "_id":0}}
    ])
))
</pre>
<div class=ans>
pp.pprint(list(db.world.aggregate([{"$match":{"population":{"$gt":200000000}}},{"$project":{"name":1, "gdp/population":{"$divide":["$gdp","$population"]}, "_id":0}}])))
</div>
</div>

<div class=q data-lang="py3">
<p class=strong>Show the name and population in millions for the countries of the continent 'South America'. Divide the population by 1000000 to get population in millions.</p>
<pre class=def>
pp.pprint(list(
    db.world.aggregate([
        {"$match":{"continent":{"$eq":"South America"}}},
        {"$project":{"name":1, "population in millions":{"$divide":["$population",1000000]}, "_id":0}}
    ])
))
</pre>
<div class=ans>
pp.pprint(list(db.world.aggregate([{"$match":{"continent":{"$eq":"South America"}}},{"$project":{"name":1, "population in millions":{"$divide":["$population",1000000]}, "_id":0}}])))
</div>
</div>

<div class=q data-lang="py3">
<p class=strong>Show the name and population for France, Germany, Italy</p>
<pre class=def>
pp.pprint(list(
    db.world.aggregate([
        {"$match":{"name":{"$in":["France", "Germany", "Italy"]}}},
        {"$project":{"name":1, "population":1, "_id":0}}
    ])
))
</pre>
<div class=ans>
pp.pprint(list(db.world.aggregate([{"$match":{"name":{"$in":["France", "Germany", "Italy"]}}},{"$project":{"name":1, "population":1, "_id":0}}])))
</div>
</div>

<div class=q data-lang="py3">
<p class=strong>Show the countries which have a name that includes the word 'United'</p>
<pre class=def>
pp.pprint(list(
    db.world.find(
        {"name":{"$regex":"\s?United\s?"}},
        {"name":1, "_id":0}
    )
))
</pre>
<div class=ans>
pp.pprint(list(db.world.find({"name":{"$regex":"\s?United\s?"}},{"name":1, "_id":0})))
</div>
</div>

<div class=q data-lang="py3">
Two ways to be big: A country is big if it has an area of more than 3 million sq km or it has a population of more than 250 million.
<p class=strong>Show the countries that are big by area or big by population. Show name, population and area</p>
<pre class=def>
pp.pprint(list(
    db.world.find(
        {"$or":[{"area":{"$gt":3000000}},{"population":{"$gt":250000000}}]},
        {"name":1,"population":1,"area":1,"_id":0}
    )
))
</pre>
<div class=ans>
pp.pprint(list(db.world.find({"$or":[{"area":{"$gt":3000000}},{"population":{"$gt":250000000}}]},{"name":1,"population":1,"area":1,"_id":0})))
</div>
</div>

<div class=q data-lang="py3">
USA and China are big in population <span class=strong>and</span> big by area. Exclude these countries.
<p class=strong>Show the countries that are big by area or big by population but not both. Show name, population and area.</p>
<pre class=def>
pp.pprint(list(
    db.world.find(
        {"$or":[
          {"area":{"$gt":3000000},"population":{"$lt":250000000}},
          {"area":{"$lt":3000000},"population":{"$gt":250000000}}
        ]},    
        {"name":1,"population":1,"area":1,"_id":0}
    )
))
</pre>
<div class=ans>
pp.pprint(list(db.world.find({"$or":[{"area":{"$gt":3000000},"population":{"$lt":250000000}},{"area":{"$lt":3000000},"population":{"$gt":250000000}}]},    {"name":1,"population":1,"area":1,"_id":0})))
</div>
</div>

<div class=q data-lang="py3">
Show the name and population in millions and the GDP in billions for the countries of the continent 'South America'. Use the ROUND function to show the values to two decimal places.<br />
Introducing [[MapReduce]]
<div class=hint title='Millions and billions'>Divide by 1000000 (6 zeros) for millions. Divide by 1000000000 (9 zeros) for billions.</div>
<p class=strong>For South America show population in millions and GDP in billions to 2 decimal places.</p>
<pre class=def>
from bson.code import Code
temp = db.world.map_reduce(
        query={"continent":"South America"},
        map=Code("function(){emit(this.name,{'gdp':this.gdp,'pop':this.population});}"), 
        reduce=Code("""function(key, values){ return values} """),
        finalize=Code("""function(k, v){
               return {
                   'pop in millions':Math.round(v['pop']*1000000)/1000000,
                   'gdp in billions':Math.round(v['gdp']*1000000000)/1000000000
               };
           }
        """),
        out={"inline":1}
)
pp.pprint(temp['results']);
</pre>
<div class=ans>
from bson.code import Code
temp = db.world.map_reduce(query={"continent":"South America"},map=Code("function(){emit(this.name, {'gdp':this.gdp,'pop':this.population});}"),reduce=Code("""function(key, values){ return values} """),finalize=Code("""function(k, v){return {'pop in millions':Math.round(v['pop']*1000000)/1000000,'gdp in billions':Math.round(v['gdp']*1000000000)/1000000000};}"""),out={"inline":1})
pp.pprint(temp['results']);
</div>
</div>

<div class=q data-lang="py3">
Show the per-capita GDP for those countries with a GDP of at least one trillion (1000000000000; that is 12 zeros). Round this value to the nearest 1000.
<p class=strong>Show per-capita GDP for the trillion dollar countries to the nearest $1000.</p>
<pre class=def>
from bson.code import Code
temp = db.world.map_reduce(
        map=Code("function(){if(this.gdp > 1000000000000)emit(this.name,{'gdp':this.gdp,'pop':this.population});}"), 
        reduce=Code("""function(key, values){ return values} """),
        finalize=Code("""function(k, v){
               return {'per-capita GDP':Math.round((v['gdp']/v['pop'])/1000)*1000};
           }
        """),
        out={"inline":1}
)
pp.pprint(temp['results']);
</pre>
<div class=ans>
from bson.code import Code
temp = db.world.map_reduce(map=Code("function(){if(this.gdp > 1000000000000)emit(this.name,{'gdp':this.gdp,'pop':this.population});}"),reduce=Code("""function(key, values){ return values} """),finalize=Code("""function(k, v){
return {'per-capita GDP':Math.round((v['gdp']/v['pop'])/1000)*1000};}"""),out={"inline":1})
pp.pprint(temp['results']);
</div>
</div>