Difference between revisions of "Round"
From NoSQLZoo
(Update to mongo shell.) |
m |
||
| (3 intermediate revisions by the same user not shown) | |||
| Line 1: | Line 1: | ||
{{TopTenTips}} | {{TopTenTips}} | ||
<div style="min-height:25em"> | <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/> | + | There are various ways of rounding in MongoDB.<br/> |
| + | Rounding is easy inside of 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/> | More information on <code>Math</code> can be found [https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Math here].<br/><br/> | ||
| − | + | In MongoDB versions prior to 3.2 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/> | |
| + | As of MongoDB 3.2, it is possible to round up, down, and truncate via <code>$ceil</code>, <code>$floor,</code> and <code>$trunc</code> respectively. | ||
</div> | </div> | ||
==MapReduce== | ==MapReduce== | ||
<div class="q nonum" data-lang="mongo"> | <div class="q nonum" data-lang="mongo"> | ||
| − | <pre class="def"> | + | <pre class="def"><nowiki> |
db.world.mapReduce( | db.world.mapReduce( | ||
| − | function(){ | + | function () { |
emit(this.name, this.population); | emit(this.name, this.population); | ||
| − | }, | + | }, |
| − | function(key, values){ | + | function (key, values) { |
return values; | return values; | ||
}, | }, | ||
{ | { | ||
| − | finalize: function(key,values){ | + | finalize: function (key,values) { |
return { | return { | ||
"population": values, | "population": values, | ||
| − | "population in millions": Math.round(values/1000000) | + | "population in millions": Math.round(values / 1000000) |
}; | }; | ||
}, | }, | ||
| Line 25: | Line 27: | ||
query: {"name": "United Kingdom"} | query: {"name": "United Kingdom"} | ||
} | } | ||
| − | ) | + | );</nowiki></pre> |
| − | </pre> | ||
</div> | </div> | ||
==Aggregate== | ==Aggregate== | ||
<div class="q nonum" data-lang="mongo"> | <div class="q nonum" data-lang="mongo"> | ||
| − | <pre class="def"> | + | <pre class="def"><nowiki> |
db.world.aggregate([ | db.world.aggregate([ | ||
{"$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":{ | + | {"$project": { |
"_id": 0, | "_id": 0, | ||
"name": 1, | "name": 1, | ||
| − | "population": '$population', | + | "population in millions": '$population', |
| − | "population in millions":{ | + | "population in millions (floored)": {"$floor": "$population"}, |
| + | "population in millions (ceiling)": {"$ceil": "$population"}, | ||
| + | "population in millions (truncated)": {"$trunc": "$population"}, | ||
| + | "population in millions (1dp with multiply / mod)":{ | ||
"$divide":[ | "$divide":[ | ||
{"$subtract":[ | {"$subtract":[ | ||
{"$multiply": ['$population', 100]}, | {"$multiply": ['$population', 100]}, | ||
| − | {"$mod": [{"$multiply": ['$population',100]}, 1]} | + | {"$mod": [{"$multiply": ['$population', 100]}, 1]} |
]}, | ]}, | ||
100 | 100 | ||
| Line 53: | Line 57: | ||
} | } | ||
}} | }} | ||
| − | ]).pretty() | + | ]).pretty();</nowiki></pre> |
| − | </pre> | ||
</div> | </div> | ||
Latest revision as of 17:45, 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();