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Difference between revisions of "MAPREDUCE Elite"

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Line 10: Line 10:
 
         _id, allegiance, faction, government, name, population, primary_economy, security, state, stations, updated_at, x, y, z
 
         _id, allegiance, faction, government, name, population, primary_economy, security, state, stations, updated_at, x, y, z
 
     systems.stations:  
 
     systems.stations:  
         allegiance, distance_to_star, economies, export_commodities,has_blackmarket, has_commodities, has_rearm, has_repair,
+
         _id, 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
 
         has_shipyard, has_outfitting, faction, government, listings, max_landing_pad, name, state, type, updated_at
 
     systems.stations.listings:  
 
     systems.stations.listings:  
         buy_price, collected_at, demand, commodity, sell_price, supply, update_count
+
         _id, buy_price, collected_at, demand, commodity, sell_price, supply, update_count
 
</pre>
 
</pre>
 
Read more about the structure here: [[Elite Document Structure]]
 
Read more about the structure here: [[Elite Document Structure]]
 
<br/><br/>
 
<br/><br/>
 +
 
==Questions==
 
==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/>
Line 24: Line 25:
 
db.commodities.mapReduce(
 
db.commodities.mapReduce(
 
   function(){
 
   function(){
     emit(1,1);
+
     emit(1, 1);
 
   },
 
   },
   function(k,v){
+
   function(k, v){
 
     return Array.sum(v);
 
     return Array.sum(v);
 
   },
 
   },
   {out:{inline:1}}
+
   {out: {inline: 1}}
)
+
);</nowiki></pre>
</nowiki></pre>
+
<pre class="ans"><nowiki>db.commodities.mapReduce(function(){emit(this.category,this.average_price);},function(k,v){return Math.round(Array.sum(v)/v.length);},{out:{inline:1}});</nowiki></pre>
<pre class="ans"><nowiki>
 
db.commodities.mapReduce(function(){emit(this.category,this.average_price);},function(k,v){return Math.round(Array.sum(v)/v.length);},{out:{inline:1}})
 
</nowiki></pre>
 
 
</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/>
Line 42: Line 40:
 
db.systems.mapReduce(
 
db.systems.mapReduce(
 
   function(){
 
   function(){
     emit(1,1);
+
     emit(1, 1);
 
   },
 
   },
   function(k,v){
+
   function(k, v){
 
     return Array.sum(v);
 
     return Array.sum(v);
 
   },
 
   },
   {out:{inline:1}}
+
   {out: {inline: 1}}
)
+
);</nowiki></pre>
</nowiki></pre>
+
<pre class="ans"><nowiki>db.systems.mapReduce(function(){if (this.allegiance!=null){emit(this.allegiance,1);}},function(k,v){return Array.sum(v);},{out:{inline:1}});</nowiki></pre>
<pre class="ans"><nowiki>
 
db.systems.mapReduce(function(){if (this.allegiance!=null){emit(this.allegiance,1);}},function(k,v){return Array.sum(v);},{out:{inline:1}})
 
</nowiki></pre>
 
 
</div>
 
</div>
 
<div class="q" data-lang="mongo" data-switches='elite'>
 
<div class="q" data-lang="mongo" data-switches='elite'>
Line 61: Line 56:
 
db.systems.mapReduce(
 
db.systems.mapReduce(
 
   function(){
 
   function(){
     emit(1,1);
+
     emit(1, 1);
 
   },
 
   },
   function(k,v){
+
   function(k, v){
 
     return Array.sum(v);
 
     return Array.sum(v);
 
   },
 
   },
   {out:{inline:1}}
+
   {out: {inline: 1}}
)
+
);</nowiki></pre>
</pre>
+
<pre class="ans"><nowiki>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}});</nowiki></pre>
<pre class="ans"><nowiki>
 
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}})
 
</nowiki></pre>
 
 
</div>
 
</div>
  
Line 85: Line 77:
 
db.systems.mapReduce(
 
db.systems.mapReduce(
 
   function(){
 
   function(){
     emit(1,1);
+
     emit(1, 1);
 
   },
 
   },
   function(k,v){
+
   function(k, v){
 
     return Array.sum(v);
 
     return Array.sum(v);
 
   },
 
   },
   {out:{inline:1}}
+
   {out: {inline: 1}}
)
+
);</nowiki></pre>
</nowiki></pre>
+
<pre class="ans"><nowiki>db.systems.mapReduce(function(){if(this.stations)for(let i=0;i<this.stations.length;i++){let t=this.stations[i];if(t.listings&&t.allegiance)for(let s=0;s<t.listings.length;s++){let n=t.listings[s];"Hydrogen Fuel"===n.commodity&&emit(t.allegiance,n.supply)}}},function(i,t){return Array.sum(t)},{out:{inline:1},limit:5e3});</nowiki></pre>
<pre class="ans"><nowiki>
 
db.systems.mapReduce(function(){if(this.stations)for(let i=0;i<this.stations.length;i++){let t=this.stations[i];if(t.listings&&t.allegiance)for(let s=0;s<t.listings.length;s++){let n=t.listings[s];"Hydrogen Fuel"===n.commodity&&emit(t.allegiance,n.supply)}}},function(i,t){return Array.sum(t)},{out:{inline:1},limit:5e3});
 
</nowiki></pre>
 
 
</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/>
 
<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/>
Line 113: Line 102:
 
db.systems.mapReduce(
 
db.systems.mapReduce(
 
   function(){
 
   function(){
     emit(1,1);
+
     emit(1, 1);
 
   },
 
   },
 
   function(k,v){
 
   function(k,v){
Line 122: Line 111:
 
     out: {inline: 1}
 
     out: {inline: 1}
 
   }
 
   }
)
+
);</nowiki></pre>
</nowiki></pre>
+
<pre class="ans"><nowiki>db.systems.mapReduce(function(){emit(this.power_control_faction,{[this.allegiance]:1});},function(_,v){let a={"Alliance":0,"Anarchy":0,"Empire":0,"Federation":0,"Independent":0};for(let i=0;i<v.length;i++){let b=v[i];a.Alliance+=b.Alliance||0;a.Anarchy+=b.Anarchy||0;a.Empire+=b.Empire||0;a.Federation+=b.Federation||0;a.Independent+=b.Independent||0;}return a;},{out:{"inline":1},query:{"power_control_faction":{"$exists":1}},sort:{"_id":1}});</nowiki></pre>
<pre class="ans"><nowiki>
 
db.systems.mapReduce(function(){emit(this.power_control_faction,{[this.allegiance]:1});},function(_,v){let a={"Alliance":0,"Anarchy":0,"Empire":0,"Federation":0,"Independent":0};for(let i=0;i<v.length;i++){let b=v[i];a.Alliance+=b.Alliance||0;a.Anarchy+=b.Anarchy||0;a.Empire+=b.Empire||0;a.Federation+=b.Federation||0;a.Independent+=b.Independent||0;}return a;},{out:{"inline":1},query:{"power_control_faction":{"$exists":1}},sort:{"_id":1}});
 
</nowiki></pre>
 
 
</div>
 
</div>
 
<div class="q" data-lang="mongo" data-switches='elite'>Our dataset doesn't contain the allegiance of a power:
 
<div class="q" data-lang="mongo" data-switches='elite'>Our dataset doesn't contain the allegiance of a power:
Line 141: Line 127:
 
db.systems.mapReduce(
 
db.systems.mapReduce(
 
   function(){
 
   function(){
     emit(1,1);
+
     emit(1, 1);
 
   },
 
   },
   function(k,v){
+
   function(k, v){
 
     return Array.sum(v);
 
     return Array.sum(v);
 
   },
 
   },
Line 153: Line 139:
 
     out: {inline: 1}
 
     out: {inline: 1}
 
   }
 
   }
)
+
);</nowiki></pre>
</nowiki></pre>
+
<pre class="ans"><nowiki>db.systems.mapReduce(function(){emit(this.power_control_faction,{[this.allegiance]:1});},function(k,v){let a={"Alliance":0,"Anarchy":0,"Empire":0,"Federation":0,"Independent":0};for(let i=0;i<v.length;i++){let b=v[i];a.Alliance+=b.Alliance||0;a.Anarchy+=b.Anarchy||0;a.Empire+=b.Empire||0;a.Federation+=b.Federation||0;a.Independent+=b.Independent||0;}return a;},{finalize:function(k,v){return Object.keys(v).reduce((a,b)=>v[a]>v[b]?a:b);},out:{"inline":1},query:{"power_control_faction":{"$exists":1}},sort:{"_id":1}});</nowiki></pre>
<pre class="ans"><nowiki>
 
db.systems.mapReduce(function(){emit(this.power_control_faction,{[this.allegiance]:1});},function(k,v){let a={"Alliance":0,"Anarchy":0,"Empire":0,"Federation":0,"Independent":0};for(let i=0;i<v.length;i++){let b=v[i];a.Alliance+=b.Alliance||0;a.Anarchy+=b.Anarchy||0;a.Empire+=b.Empire||0;a.Federation+=b.Federation||0;a.Independent+=b.Independent||0;}return a;},{finalize:function(k,v){return Object.keys(v).reduce((a,b)=>v[a]>v[b]?a:b);},out:{"inline":1},query:{"power_control_faction":{"$exists":1}},sort:{"_id":1}});
 
</nowiki></pre>
 
 
</div>
 
</div>
 +
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 +
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Latest revision as of 13:48, 17 October 2018

Introducing the elite database

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: 
        _id, 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: 
        _id, 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 are not populated and will have null population fields, 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 each faction? Limit your query to the first 5000 stations.

The amount of stations in a system and the amount of listings to a station aren't fixed. query can be used to ensure that they exist.

db.systems.mapReduce(
  function(){
    emit(1, 1);
  },
  function(k, v){
    return Array.sum(v);
  },
  {out: {inline: 1}}
);
db.systems.mapReduce(function(){if(this.stations)for(let i=0;i<this.stations.length;i++){let t=this.stations[i];if(t.listings&&t.allegiance)for(let s=0;s<t.listings.length;s++){let n=t.listings[s];"Hydrogen Fuel"===n.commodity&&emit(t.allegiance,n.supply)}}},function(i,t){return Array.sum(t)},{out:{inline:1},limit:5e3});
A power_control_faction or Power is an individual or organisation who is in control of a system.

These powers have allegiance to a faction, but the systems they control do not nescessarily have the same allegiance that 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.systems.mapReduce(
  function(){
    emit(1, 1);
  },
  function(k,v){
    return Array.sum(v);
  },
  {
    query: {"power_control_faction": {"$exists": 1}},
    out: {inline: 1}
  }
);
db.systems.mapReduce(function(){emit(this.power_control_faction,{[this.allegiance]:1});},function(_,v){let a={"Alliance":0,"Anarchy":0,"Empire":0,"Federation":0,"Independent":0};for(let i=0;i<v.length;i++){let b=v[i];a.Alliance+=b.Alliance||0;a.Anarchy+=b.Anarchy||0;a.Empire+=b.Empire||0;a.Federation+=b.Federation||0;a.Independent+=b.Independent||0;}return a;},{out:{"inline":1},query:{"power_control_faction":{"$exists":1}},sort:{"_id":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.

To achieve this, you'll need to use the finalize: function(k, v){} in the third argument to find the key with the largest value.

{
    "_id" : "Zemina Torval",
    "value" : "Empire"
}
db.systems.mapReduce(
  function(){
    emit(1, 1);
  },
  function(k, v){
    return Array.sum(v);
  },
  {
    finally: function(k, v){
      return v;
    },
    query: {"power_control_faction": {"$exists": 1}},
    out: {inline: 1}
  }
);
db.systems.mapReduce(function(){emit(this.power_control_faction,{[this.allegiance]:1});},function(k,v){let a={"Alliance":0,"Anarchy":0,"Empire":0,"Federation":0,"Independent":0};for(let i=0;i<v.length;i++){let b=v[i];a.Alliance+=b.Alliance||0;a.Anarchy+=b.Anarchy||0;a.Empire+=b.Empire||0;a.Federation+=b.Federation||0;a.Independent+=b.Independent||0;}return a;},{finalize:function(k,v){return Object.keys(v).reduce((a,b)=>v[a]>v[b]?a:b);},out:{"inline":1},query:{"power_control_faction":{"$exists":1}},sort:{"_id":1}});

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