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


From NoSQLZoo
Jump to: navigation, search

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.

  function () {
    emit(, 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"}

  {"$match": {"name": "United Kingdom"}},
  {"$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)":{
          {"$multiply": ['$population', 100]},
          {"$mod": [{"$multiply": ['$population', 100]}, 1]}