MAPREDUCE Elite
From NoSQLZoo
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 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.
db.commodities.mapReduce(
function(){
emit(1,1);
},
function(k,v){
return Array.sum(v);
},
{out:{inline:1}}
)
db.commodities.mapReduce(function(){emit(this.category,this.average_price);},function(k,v){return Math.round(Array.sum(v)/v.length);},{out:{inline:1}})
Each system has an
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(){
emit(1,1);
},
function(k,v){
return Array.sum(v);
},
{out:{inline:1}}
)
db.systems.mapReduce(function(){if (this.allegiance!=null){emit(this.allegiance,1);}},function(k,v){return Array.sum(v);},{out:{inline:1}})What are the populations of the three main factions?
["Alliance","Federation","Empire"]
Some systems have no populations, make sure to exclude them using
!isNaN().db.systems.mapReduce(
function(){
emit(1,1);
},
function(k,v){
return Array.sum(v);
},
{out:{inline:1}}
)
db.systems.mapReduce(function(){if (!isNaN(this.population) && 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
How much Hydrogen Fuel is owned by stations in systems. Limit your query to the first 5000 stations.
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.commodities.mapReduce(
function(){
emit(1,1);
},
function(k,v){
return Array.sum(v);
},
{out:{inline:1}}
)
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}
);
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.
At the time of writing Zemina Torval is allied with the Empire and controls 47 systems.
{ '_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
db.commodities.mapReduce(
function(){
emit(1,1);
},
function(k,v){
return Array.sum(v);
},
{out:{inline:1}}
)
db.systems.mapReduce(
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;
}
},
function(k,vs){
let a = vs[0];
for(let i=1; i < vs.length; i++){
let 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},
query: {"power_control_faction": {"$exists":1}}
}
)
Our dataset doesn't contain the allegiance of a power:
Using the result from the previous question, guess the power's allegiance by the faction that the majority of their systems follow.
Zemina Torval: Empire(39.0)db.commodities.mapReduce(
function(){
emit(1,1);
},
function(k,v){
return Array.sum(v);
},
{out:{inline:1}}
)
temp = db.systems.map_reduce(query={"power_control_faction":{"$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)+")")