Cookies help us deliver our services. By using our services, you agree to our use of cookies. More information

Difference between revisions of "Round"

From NoSQLZoo
Jump to: navigation, search
(Update for 3.6)
m
Line 44: Line 44:
 
     "_id": 0,
 
     "_id": 0,
 
     "name": 1,
 
     "name": 1,
     "population": '$population',
+
     "population in millions": '$population',
 
     "population in millions (floored)":{ "$floor": "$population"},
 
     "population in millions (floored)":{ "$floor": "$population"},
 
     "population in millions (ceiling)":{ "$ceil": "$population"},
 
     "population in millions (ceiling)":{ "$ceil": "$population"},

Revision as of 04:43, 6 April 2018

There are various ways of rounding in MongoDB.
Rounding is easy inside of a MapReduce as it is possible to use the Math object provided by JavaScript.
More information on Math can be found here.

In MongoDB versions prior to 3.2 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.
As of MongoDB 3.2, it is possible to round up, down, and truncate via $ceil, $floor, and $trunc respectively.

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]}
  }},
  {"$project":{
    "_id": 0,
    "name": 1,
    "population in millions": '$population',
    "population in millions (floored)":{ "$floor": "$population"},
    "population in millions (ceiling)":{ "$ceil": "$population"},
    "population in millions (truncated)":{ "$trunc": "$population"},
    "population in millions (1dp with multiply / mod)":{
      "$divide":[
        {"$subtract":[
          {"$multiply": ['$population', 100]},
          {"$mod": [{"$multiply": ['$population',100]}, 1]}
        ]},
        100
      ]
    }
  }}
]).pretty()