Round
From NoSQLZoo
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();