View source for MAPREDUCE Elite

==Introducing the elite database **WORK IN PROGRESS==
These questions will introduce the "elite" database, which contains data about the video game [https://www.elitedangerous.com/ Elite Dangerous]<br/>
<code>from bson.code import Code</code> has been added to the setup so that you no longer need to include it in your answer.<br/><br/>
There are two collections, <code>commodities</code> and <code>systems</code>. Inside <code>systems</code> there is are nested documents called <code>stations</code><br/>
A <b>system</b> has many <b>stations</b>, and a <b>station</b> has many trade <code>listings</code><br/><br/>
Keys used in this database.
<pre>
    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
        
</pre>
Read more about the structure here: [[Elite Document Structure]]
<br/><br/>

==Questions==
<div class=q data-lang="mongo" data-switches='elite'>The <code>commodities</code> collection contains the <code>name</code> and <code>average_price</code> of each commodity.<br/>
There are 99 unique commodities and 15 categories.
<p class="strong">Find the average price of each category, round to the nearest whole number</p>
<pre class=def>
db.commodities.findOne()
</pre>
<div class="ans">
db.commodities.mapReduce(
  function(){emit(this.category,this.average_price);},
  function(k,v){return Math.round(Array.sum(v)/v.length);},
  {out:{inline:1}}
)
</div>
</div>

<div class=q data-lang="mongo" data-switches='elite'>Each system has an <code>allegiance</code>. There are three main factions: <b>The Federation</b>, <b>The Empire</b>, and <b>The Alliance</b>.<br/>
<p>Non-populated systems without stations do not have an allegiance, and should be ignored.</p> 
<p class=strong>Show the amount of systems following each type of allegiance.</p>
<pre class=def>
</pre>
<div class="ans">
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}}
)  
</div>
</div>

<div class=q data-lang="mongo" data-switches='elite'>
<p class="strong">What are the populations of the three main factions?</p>
<div class=hint title="Three main factions">["Alliance","Federation","Empire"]</div>
<pre class=def>
</pre>
<div class="ans">
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}}
)
</div>
</div>

==Harder Questions==
<div class=q data-lang="mongo" data-switches='elite'>How much Hydrogen Fuel is owned by stations in systems that are allied with the three main factions? Limit your query to the first 5000 stations.
<div class="hint" title="hint">
The amount of stations <b>and</b> the amount of listings aren't fixed, you'll need to <code>query</code> to ensure that they exist and find a way of iterating through them in your <code>map</code> stage.
</div>
<pre class=def>
</pre>
<div class="ans">
temp = db.systems.map_reduce( limit=5000, query={"allegiance":{"$in":["Alliance","Empire","Federation"]},"stations.listings.commodity":"Hydrogen Fuel","stations.listings.supply":{"$exists":1}}, map=Code("""function(){ for(var i in this.stations) for(var j in this.stations[i].listings) emit(this.allegiance,this.stations[i].listings[j].supply) }"""), reduce=Code("""function(k,vs){var t = 0;vs.forEach(function(v){t += v});return t;} """), out={"inline":1} ); 
pp.pprint(temp['results']);
</div>
</div>

<div class=q data-lang="mongo" data-switches='elite'>A <code>power_control_faction</code> or <b>Power</b> is an individual or organisation who is in control of a system.<br/>
These powers have allegiances, but the systems they control do not nescessarily have the same allegiance as they do.
<div class="hint" title="Example"> At the time of writing <b>Zemina Torval</b> is allied with the <b>Empire</b> and controls <b>47</b> systems.<br/>
<pre>
    {   '_id': 'Zemina Torval',
        'value': {   'alliance': 0.0,
                     'anarchy': 0.0,
                     'empire': 39.0,
                     'federation': 3.0,
                     'independent': 5.0}}]
</pre>
</div>
<p class="strong">Show the allegiance of each of the power's systems</p>
<pre class=def>
</pre>
<div class="ans">
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']);
</div>
</div>

<div class=q data-lang="mongo" data-switches='elite'>Our dataset doesn't contain the allegiance of a power:
<p class="strong">Using the result from the previous question, guess the power's allegiance by the faction that the majority of their systems follow.</p>
<div class="hint" title="Example"><code>Zemina Torval: Empire(39.0)</code></div>
<pre class=def>
</pre>
<div class="ans">
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)+")")
</div>
</div>