Difference between revisions of "Round"

Revision as of 02:46, 6 April 2018

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Rounding is easy inside a MapReduce as it is possible to use the Math object provided by JavaScript.
More information on Math can be found here.

At the time of writing the aggregation() method has no rounding functions, though it is still doable with $mod and $multiply, as shown here by the lead project manager at MongoDB.

MapReduce

db.world.mapReduce(
  function(){
    emit(this.name, this.population);
  }, 
  function(key, values){
    return values;
  },
  {
    finalize: function(key,values){
      return {
          "population": values,
          "population in millions": Math.round(values/1000000)
      };
    },
    out: {inline: 1},
    query: {"name": "United Kingdom"}
  }
)

Aggregate

db.world.aggregate([
  {"$match": {"name": "United Kingdom"}},
  {"$project":{
    "_id": 1,
    "name": 1,
    "population":{"$divide": ["$population", 1000000]}
  }},
  {"$project":{
    "_id": 0,
    "name": 1,
    "population": '$population',
    "population in millions":{
      "$divide":[
        {"$subtract":[
          {"$multiply": ['$population', 100]},
          {"$mod": [{"$multiply": ['$population',100]}, 1]}
        ]},
        100
      ]
    }
  }}
]).pretty()

@@ Line 1: / Line 1: @@
-<pre class=setup>
-#ENCODING
-import io
-import sys
-sys.stdout = io.TextIOWrapper(sys.stdout.buffer, encoding='utf-16')
-#MONGO
-from pymongo import MongoClient
-client = MongoClient()
-client.progzoo.authenticate('scott','tiger')
-db = client['progzoo']
-#PRETTY
-import pprint
-pp = pprint.PrettyPrinter(indent=4)
-#CODE
-from bson.code import Code
-</pre>
 {{TopTenTips}}
 <div style="min-height:25em">
 Rounding is easy inside a <code>MapReduce</code> as it is possible to use the <code>Math</code> object provided by JavaScript.<br/>
 More information on <code>Math</code> can be found [https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Math here].<br/><br/>
-At the time of writing the <code>aggregation()</code> method has no rounding functions, though it is still doable with <code>$mod</code> and <code>$multiply</code>, as shown [http://www.kamsky.org/stupid-tricks-with-mongodb/rounding-numbers-in-aggregation-framework here] by the lead project manager at MongoDB<br/>.
+At the time of writing the <code>aggregation()</code> method has no rounding functions, though it is still doable with <code>$mod</code> and <code>$multiply</code>, as shown [http://www.kamsky.org/stupid-tricks-with-mongodb/rounding-numbers-in-aggregation-framework here] by the lead project manager at MongoDB.<br/>
 </div>
 ==MapReduce==
-<div class="q nonum" data-lang="py3">
+<div class="q nonum" data-lang="mongo">
-<pre class=def>
+<pre class="def">
-temp = db.world.map_reduce(
+db.world.mapReduce(
-        query={"name":"United Kingdom"},
+  function(){
-        map=Code("function(){emit(this.name, this.population)}"),
+    emit(this.name, this.population);
-        reduce=Code("function(key, values){return values}"),
+  },
-        finalize=Code("function(key,values){return Math.round(values/1000000)}"),
+  function(key, values){
-        out={"inline":1},
+    return values;
-)
+  },
-pp.pprint(
+  {
-   temp["results"]
+    finalize: function(key,values){
+      return {
+          "population": values,
+          "population in millions": Math.round(values/1000000)
+      };
+    },
+    out: {inline: 1},
+    query: {"name": "United Kingdom"}
+  }
 )
 </pre>
@@ Line 38: / Line 30: @@
 ==Aggregate==
-<div class="q nonum" data-lang="py3">
+<div class="q nonum" data-lang="mongo">
-<pre class=def>
+<pre class="def">
-pp.pprint(list(
+db.world.aggregate([
-    db.world.aggregate([
+  {"$match": {"name": "United Kingdom"}},
-        {"$match": {"name":"United Kingdom"}},
+  {"$project":{
-        {"$project":{
+    "_id": 1,
-            "_id":1, "name":1, "population":{"$divide":["$population",1000000]}
+    "name": 1,
-        }},
+    "population":{"$divide": ["$population", 1000000]}
-        {"$project":{
+  }},
-            "_id":0, "name":1, "population in millions":{"$divide":[
+  {"$project":{
-                {"$subtract":[
+    "_id": 0,
-                    {"$multiply":['$population',100]},
+    "name": 1,
-                    {"$mod":[{"$multiply":['$population',100]}, 1]}
+    "population": '$population',
-                    ]},100
+    "population in millions":{
-            ]}
+      "$divide":[
-        }}
+        {"$subtract":[
-    ])
+          {"$multiply": ['$population', 100]},
-))
+          {"$mod": [{"$multiply": ['$population',100]}, 1]}
+        ]},
+      ]
+    }
+  }}
+]).pretty()
 </pre>
 </div>