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> | |||
<div class="def">db.world.count({"continent":"Africa"})</div> | |||
</div> | </div> | ||
<div class="q nonum" data-lang="mongo">$sum | <div class="q nonum" data-lang="mongo"><code>$sum</code> | ||
<div class="def"> | <div class="def"> | ||
db.world.aggregate([ | db.world.aggregate([ | ||
{"$group":{ | |||
"_id": "$continent", | |||
"sum of populations": {$sum: "$population"}, | |||
"count of countries": {$sum: 1} | |||
}} | |||
]) | ]) | ||
</div> | </div> | ||
</div> | </div> | ||
<div class="q nonum" data-lang="mongo">Array.sum() | <div class="q nonum" data-lang="mongo"><code>Array.sum()</code> | ||
<div class="def"> | <div class="def"> | ||
db.world.mapReduce( | db.world.mapReduce( | ||
function(){ | |||
emit(this.continent, this.population); | |||
}, | |||
function(k,v){ | |||
return Array.sum(v); | |||
}, | |||
{ | |||
out:{inline:1} | |||
} | |||
) | ) | ||
</div> | </div> | ||
</div> | </div> | ||
Revision as of 02:35, 6 April 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}
}
)