Difference between revisions of "MAPREDUCE Elite"

Revision as of 18:45, 21 March 2018

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.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

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']);

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)

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)+")")

@@ Line 22: / Line 22: @@
 ==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/>
+<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>
+<p class="strong">Find the average price of each category, round to the nearest whole number.</p>
-<pre class=def>
+<pre class="def">
-db.commodities.mapReduce()
-</pre>
-<div class="ans">
 db.commodities.mapReduce(
-   function(){emit(this.category,this.average_price);},
+   function(){
-   function(k,v){return Math.round(Array.sum(v)/v.length);},
+    emit(1,1);
+  },
+   function(k,v){
+    return Array.sum(v);
+  },
    {out:{inline:1}}
 )
+</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/>
-<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>
+<p class="strong">Show the amount of systems following each type of allegiance.</p>
-<pre class=def>
+<pre class="def">
-</pre>
-<div class="ans">
 db.systems.mapReduce(
    function(){
-if (this.allegiance != null ){//&& this.allegiance != "Independent" && this.allegiance != "Anarchy") {
+    emit(1,1);
-emit(this.allegiance, 1);}},
+  },
-   function(k,v){return Array.sum(v);},
+   function(k,v){
+    return Array.sum(v);
+  },
    {out:{inline:1}}
 )
+</pre>
+<div class="ans">db.systems.mapReduce(function(){if (this.allegiance!=null){emit(this.allegiance,1);}},function(k,v){return Array.sum(v);},{out:{inline:1}})</div>
 </div>
-</div>
+<div class="q" data-lang="mongo" data-switches='elite'>
-<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>
+<div class="hint" title="Three main factions">["Alliance","Federation","Empire"]</div>
-<pre class=def>
+<div class="hint" title="NaN?">Some systems have no populations, make sure to exclude them using <code>!isNaN()</code>.</div>
-</pre>
+<pre class="def">
-<div class="ans">
 db.systems.mapReduce(
    function(){
-if (this.allegiance != null ){//&& this.allegiance != "Independent" && this.allegiance != "Anarchy") {
+    emit(1,1);
-emit(this.allegiance, this.population);}},
+  },
-   function(k,v){return Array.sum(v);},
+   function(k,v){
+    return Array.sum(v);
+  },
    {out:{inline:1}}
 )
-</div>
+</pre>
+<div class="ans">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}})</div>
 </div>