Difference between revisions of "MAPREDUCE Elite"

Revision as of 15:04, 25 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.elite.authenticate('scott','tiger')
db = client['elite']
#PRETTY
import pprint
pp = pprint.PrettyPrinter(indent=4)
#JS
from bson.code import Code

Introducing the elite database **WORK IN PROGRESS

These questions will introduce the "elite" database, which contains data about the video game Elite Dangerous

There are two collections, commodities and systems. Inside systems there is are nested documents called stations
A system has many stations, and a station has many trade listings

Keys used in this database.

    commodities: 
        _id, average_price, category, name
    systems: 
        _id, allegiance, faction, government, name, population, primary_economy, security, state, stations, updated_at, x, y, z

    systems.stations: 
        allegiance, distance_to_star, economies, export_commodities,has_blackmarket, has_commodities, has_rearm, has_repair,
        has_shipyard, has_outfitting, faction, government, listings, max_landing_pad, name, state, type, updated_at

    systems.stations.listings: 
        buy_price, collected_at, demand, commodity, sell_price, supply, update_count

Read more about the structure here: Elite Document Structure

Questions

The commodities collection contains the name and average_price of each commodity.

There are 99 unique commodities and 15 categories.

Find the average price of each category, round to the nearest whole number

pp.pprint(
    db.commodities.find_one()
)

from bson.code import Code;temp = db.commodities.map_reduce( map=Code("function(){emit(this.category,this.average_price)}"), reduce=Code("""function(key,values){var total = 0;for (var i = 0; i < values.length; i++){total += values[i];}return Math.round(total/values.length);} """),out={"inline":1} );pp.pprint(temp['results'])

There are many types of Government. Show the total population of all the systems following each type.

It's not possible to emit on a field that doesn't exist. Use query to only include documents where the fields you need exist.

temp = db.systems.map_reduce( query={"government":{"$exists":1},"population":{"$exists":1}}, map=Code("function(){emit(this.government,this.population)}"), reduce=Code("""function(key,values){var total = 0;values.forEach(function(value){total += value;});return total;} """), out={"inline":1} );pp.pprint(temp['results'])

Each system has an allegiance. There are three main factions: The Federation, The Empire, and The Alliance.

The Alliance consists of independent systems, though an independent system is not necessarily part of The Alliance. In such a case their allegiance will be stored as "Independent"
There are a few systems that come under Anarchy. Non-populated systems without stations do not have an allegiance, and should be ignored.

Show the amount of systems following each type of allegiance.

temp = db.systems.map_reduce( query={"allegiance": {"$ne":None}}, map=Code("function(){emit(this.allegiance, 1)}"), reduce=Code("""function(key,values){var total = 0;values.forEach(function(value){total += value;});return total;} """), out={"inline":1} );pp.pprint(temp['results'])

Harder Questions

A power_control_faction or Power is an individual or organisation who is in control of a system.

These powers have allegiances, but the systems they control do not nescessarily have the same allegiance as they do.

Example: At the time of writing Zemina Torval is allied with the Empire and controls 47 systems.
    39 are allied to The Empire
    3 are allied to The Federation
    5 systems are Independent

Long live the Emperor!
'Arissa Lavigny-Duval','Aisling Duval','Denton Patreus' and 'Zemina Torval' all support the empire, show the amount of systems they control that aren't allied to the Empire.

temp = db.systems.map_reduce( query={"power_control_faction":{"$in":['Arissa Lavigny-Duval','Aisling Duval','Denton Patreus','Zemina Torval']},"allegiance":{"$ne":"Empire"}}, map=Code("""function(){ emit({"power_control_faction":this.power_control_faction,"allegiance":this.allegiance},1) }"""), reduce=Code("""function(k,vs){var t = 0;vs.forEach(function(v){t += v});return t} """), out={"inline":1} ); pp.pprint(temp['results']);

@@ Line 51: / Line 51: @@
 <div class=q data-lang="py3">
-<p class="strong">There are many types of Government. Show the amount of people for each type.</p>
+<p class="strong">There are many types of Government. Show the total population of all the systems following each type.</p>
 <div class="hint" title="Assertion errors, dealing with non-existent values">
 It's not possible to <code>emit</code> on a field that doesn't exist. Use <code>query</code> to only include documents where the fields you need exist.