MAPREDUCE Elite
Introducing the elite database **WORK IN PROGRESS
These questions will introduce the "elite" database, which contains data about the video game Elite Dangerous
from bson.code import Code has been added to the setup so that you no longer need to include it in your answer.
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
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
db.commodities.mapReduce()
db.commodities.mapReduce(
function(){emit(this.category,this.average_price);},
function(k,v){return Math.round(Array.sum(v)/v.length);},
{out:{inline:1}}
)
allegiance. There are three main factions: The Federation, The Empire, and The Alliance.Non-populated systems without stations do not have an allegiance, and should be ignored.
Show the amount of systems following each type of allegiance.
db.systems.mapReduce(
function(){
if (this.allegiance != null ){//&& this.allegiance != "Independent" && this.allegiance != "Anarchy") { emit(this.allegiance, 1);}},
function(k,v){return Array.sum(v);},
{out:{inline:1}}
)
What are the populations of the three main factions?
db.systems.mapReduce(
function(){
if (this.allegiance != null ){//&& this.allegiance != "Independent" && this.allegiance != "Anarchy") { emit(this.allegiance, this.population);}},
function(k,v){return Array.sum(v);},
{out:{inline:1}}
)
Harder Questions
The amount of stations and the amount of listings aren't fixed, you'll need to query to ensure that they exist and find a way of iterating through them in your map stage.
db.systems.mapReduce(
function(){
if (this.stations){
for(var i=0;i<this.stations.length;i++){
var station = this.stations[i];
if (station.listings && station.allegiance){
for(var j=0;j<station.listings.length;j++){
var comm = station.listings[j];
if (comm.commodity==='Hydrogen Fuel')
emit(station.allegiance,comm.supply);
}
}else{
//emit('no listing',1);
}
}
}else{
//emit('no stations',1);
}
},
function(k,v){return Array.sum(v);},
{out:{inline:1},limit:5000}
);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.
{ '_id': 'Zemina Torval',
'value': { 'alliance': 0.0,
'anarchy': 0.0,
'empire': 39.0,
'federation': 3.0,
'independent': 5.0}}]
Show the allegiance of each of the power's systems
temp = db.systems.map_reduce(query={"power_control_faction":{"$exists":1}},map=Code("""function(){switch(this.allegiance){case "Alliance":emit(this.power_control_faction,{alliance:1,anarchy:0,empire:0,federation:0,independent:0});break;case "Anarchy":emit(this.power_control_faction,{alliance:0,anarchy:1,empire:0,federation:0,independent:0});break; case "Empire":emit(this.power_control_faction,{alliance:0,anarchy:0,empire:1,federation:0,independent:0});break;case "Federation":emit(this.power_control_faction,{alliance:0,anarchy:0,empire:0,federation:1,independent:0});break;case "Independent":emit(this.power_control_faction,{alliance:0,anarchy:0,empire:0,federation:0,independent:1});break;}}"""),reduce=Code("""function(k,vs){var a=vs[0];for(var i=1;i<vs.length;i++){var b=vs[i];a.alliance+=b.alliance;a.anarchy+=b.anarchy;a.empire+=b.empire;a.federation+=b.federation;a.independent+=b.independent;}return a}"""),out={"inline":1}); pp.pprint(temp['results']);
Using the result from the previous question, guess the power's allegiance by the faction that the majority of their systems follow.
Zemina Torval: Empire(39.0)temp = db.systems.map_reduce(query={"power_control_faction":{"$exists":1}},map=Code("""function(){switch(this.allegiance){case "Alliance":emit(this.power_control_faction,{alliance:1,anarchy:0,empire:0,federation:0,independent:0});break;case "Anarchy":emit(this.power_control_faction,{alliance:0,anarchy:1,empire:0,federation:0,independent:0});break; case "Empire":emit(this.power_control_faction,{alliance:0,anarchy:0,empire:1,federation:0,independent:0});break;case "Federation":emit(this.power_control_faction,{alliance:0,anarchy:0,empire:0,federation:1,independent:0});break;case "Independent":emit(this.power_control_faction,{alliance:0,anarchy:0,empire:0,federation:0,independent:1});break;}}"""),reduce=Code("""function(k,vs){var a=vs[0];for(var i=1;i<vs.length;i++){var b=vs[i];a.alliance+=b.alliance;a.anarchy+=b.anarchy;a.empire+=b.empire;a.federation+=b.federation;a.independent+=b.independent;}return a}"""),out={"inline":1}); for power in temp['results']:
max = 0;
key = "";
#print(power['value'])
for id in power['value']:
if (power['value'][id] > max):
max = power['value'][id]
key = id
print(power['_id']+": "+key+"("+str(max)+")")