$stdDevPop operator in MongoDB - Find standard deviation from documents

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$stdDevPop operator in MongoDB >
$stdDevPop operator returns the standard deviation from documents in the collection in MongoDB.
1) First let's create insert documents in collection in MongoDB


1.1) First, Let's create new collection and insert document >
db.employee.insert({_id : 1,  firstName:"ank", salary : 1000 })
db.employee.insert({_id : 2,  firstName:"ank", salary : 2000 })
db.employee.insert({_id : 3,  firstName:"sag", salary : 3000 })
db.employee.insert({_id : 4,  firstName:"sag", salary : 4000 })
db.employee.insert({_id : 5,  firstName:"neh", salary : 5000 })
Above will create collection (or table) (if collection already exists it will insert documents in it).


1.2) FIND > Query all documents of collection using find() method>
db.employee.find()
Output>
{ "_id" : 1, "firstName" : "ank", "salary" : 1000 }
{ "_id" : 2, "firstName" : "ank", "salary" : 2000 }
{ "_id" : 3, "firstName" : "sag", "salary" : 3000 }
{ "_id" : 4, "firstName" : "sag", "salary" : 4000 }
{ "_id" : 5, "firstName" : "neh", "salary" : 5000 }


2) Find standard deviation on salary of employee with same firstName in collection in MongoDB >


Step 2.1 - We will use aggregate() method, $group operator and $stdDevPop operator to
Step 2.2 -  group employee by firstName and find standard deviation of each group.


db.employee.aggregate([{$group : {_id : "$firstName", standardDeviation : {$stdDevPop : "$salary"}}}])
Note :  $stdDevPop can be used in MongoDB 3.2 or above.

3) Summary -
So in this MongoDB tutorial we learned $stdDevPop operator in MongoDB.
$stdDevPop operator returns the standard deviation from documents in the collection in MongoDB.
Find standard deviation of employee with same firstName in collection in MongoDB >
db.employee.aggregate([{$group : {_id : "$firstName", standardDeviation : {$stdDevPop : "$salary"}}}])


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