Round: Difference between revisions
From NoSQLZoo
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==MapReduce== | ==MapReduce== | ||
<div class="q nonum" data-lang="mongo"> | <div class="q nonum" data-lang="mongo"> | ||
<pre class="def"> | <pre class="def"><nowiki> | ||
db.world.mapReduce( | db.world.mapReduce( | ||
function(){ | function () { | ||
emit(this.name, this.population); | emit(this.name, this.population); | ||
}, | }, | ||
function(key, values){ | function (key, values) { | ||
return values; | return values; | ||
}, | }, | ||
{ | { | ||
finalize: function(key,values){ | finalize: function (key,values) { | ||
return { | return { | ||
"population": values, | "population": values, | ||
"population in millions": Math.round(values/1000000) | "population in millions": Math.round(values / 1000000) | ||
}; | }; | ||
}, | }, | ||
| Line 27: | Line 27: | ||
query: {"name": "United Kingdom"} | query: {"name": "United Kingdom"} | ||
} | } | ||
) | );</nowiki></pre> | ||
</pre> | |||
</div> | </div> | ||
==Aggregate== | ==Aggregate== | ||
<div class="q nonum" data-lang="mongo"> | <div class="q nonum" data-lang="mongo"> | ||
<pre class="def"> | <pre class="def"><nowiki> | ||
db.world.aggregate([ | db.world.aggregate([ | ||
{"$match": {"name": "United Kingdom"}}, | {"$match": {"name": "United Kingdom"}}, | ||
{"$project":{ | {"$project": { | ||
"_id": 1, | "_id": 1, | ||
"name": 1, | "name": 1, | ||
"population":{"$divide": ["$population", 1000000]} | "population": {"$divide": ["$population", 1000000]} | ||
}}, | }}, | ||
{"$project":{ | {"$project": { | ||
"_id": 0, | "_id": 0, | ||
"name": 1, | "name": 1, | ||
"population in millions": '$population', | "population in millions": '$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"}, | ||
"population in millions (truncated)":{ "$trunc": "$population"}, | "population in millions (truncated)": {"$trunc": "$population"}, | ||
"population in millions (1dp with multiply / mod)":{ | "population in millions (1dp with multiply / mod)":{ | ||
"$divide":[ | "$divide":[ | ||
{"$subtract":[ | {"$subtract":[ | ||
{"$multiply": ['$population', 100]}, | {"$multiply": ['$population', 100]}, | ||
{"$mod": [{"$multiply": ['$population',100]}, 1]} | {"$mod": [{"$multiply": ['$population', 100]}, 1]} | ||
]}, | ]}, | ||
100 | 100 | ||
| Line 58: | Line 57: | ||
} | } | ||
}} | }} | ||
]).pretty() | ]).pretty();</nowiki></pre> | ||
</pre> | |||
</div> | </div> | ||
Revision as of 16:44, 18 July 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();