Sum and Count: Difference between revisions
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<code>count()</code> is a cursor method that takes a query and returns a number equal to the amount of documents that matched the query.<br/> | <code>count()</code> is a cursor method that takes a query and returns a number equal to the amount of documents that matched the query.<br/> | ||
<code>$sum</code> is an aggregation operator availible in the <code>$group</code> stage, that can be used to both sum values and count the number of documents.<br/> | <code>$sum</code> is an aggregation operator availible in the <code>$group</code> stage, that can be used to both sum values and count the number of documents.<br/> | ||
mapReduce can produce a sum or a count during the results stage by using JavaScript. | <code>mapReduce</code> can produce a sum or a count during the results stage by using JavaScript. | ||
</div> | </div> | ||
<div class="q nonum" data-lang="mongo"><code>.count()</code> | |||
<pre class="def"><nowiki>db.world.count({"continent": "Africa"});</nowiki></pre> | |||
</div> | </div> | ||
<div class="q nonum" data-lang="mongo">$sum | <div class="q nonum" data-lang="mongo"><code>$sum</code> | ||
< | <pre class="def"><nowiki> | ||
db.world.aggregate([ | db.world.aggregate([ | ||
{"$group": { | |||
"_id": "$continent", | |||
"sum of populations": {$sum: "$population"}, | |||
"count of countries": {$sum: 1} | |||
}} | |||
]) | ]);</nowiki></pre> | ||
</ | |||
</div> | </div> | ||
<div class="q nonum" data-lang="mongo">Array.sum() | <div class="q nonum" data-lang="mongo"><code>Array.sum()</code> | ||
< | <pre class="def"><nowiki> | ||
db.world.mapReduce( | db.world.mapReduce( | ||
function () { | |||
emit(this.continent, this.population); | |||
}, | |||
) | function (k, v) { | ||
</ | return Array.sum(v); | ||
}, | |||
{ | |||
out: {inline: 1} | |||
} | |||
); | |||
</nowiki></pre> | |||
</div> | </div> | ||
Latest revision as of 16:41, 18 July 2018
There are many ways to do this in MongoDB.
count() is a cursor method that takes a query and returns a number equal to the amount of documents that matched the query.
$sum is an aggregation operator availible in the $group stage, that can be used to both sum values and count the number of documents.
mapReduce can produce a sum or a count during the results stage by using JavaScript.
.count()
db.world.count({"continent": "Africa"});
$sum
db.world.aggregate([
{"$group": {
"_id": "$continent",
"sum of populations": {$sum: "$population"},
"count of countries": {$sum: 1}
}}
]);
Array.sum()
db.world.mapReduce(
function () {
emit(this.continent, this.population);
},
function (k, v) {
return Array.sum(v);
},
{
out: {inline: 1}
}
);