$stddevsamp
The $stddevsamp operator calculates the standard deviation of a specified sample of values and not the entire population
$stddevsamp
The $stddevsamp operator calculates the standard deviation by taking a specified sample of the values of a field. The standard deviation is calculated by taking a random sample of the specified size. If a precise standard deviation is needed, $stdDevPop must be used instead.
Parameters
| Parameter | Description |
|---|---|
fieldName | The field whose values are used to calculate the standard deviation of the specified sample size |
Examples
Consider this sample document from the stores collection.
{
"_id": "0fcc0bf0-ed18-4ab8-b558-9848e18058f4",
"name": "First Up Consultants | Beverage Shop - Satterfieldmouth",
"location": {
"lat": -89.2384,
"lon": -46.4012
},
"staff": {
"totalStaff": {
"fullTime": 8,
"partTime": 20
}
},
"sales": {
"totalSales": 75670,
"salesByCategory": [
{
"categoryName": "Wine Accessories",
"totalSales": 34440
},
{
"categoryName": "Bitters",
"totalSales": 39496
},
{
"categoryName": "Rum",
"totalSales": 1734
}
]
},
"promotionEvents": [
{
"eventName": "Unbeatable Bargain Bash",
"promotionalDates": {
"startDate": {
"Year": 2024,
"Month": 6,
"Day": 23
},
"endDate": {
"Year": 2024,
"Month": 7,
"Day": 2
}
},
"discounts": [
{
"categoryName": "Whiskey",
"discountPercentage": 7
},
{
"categoryName": "Bitters",
"discountPercentage": 15
},
{
"categoryName": "Brandy",
"discountPercentage": 8
},
{
"categoryName": "Sports Drinks",
"discountPercentage": 22
},
{
"categoryName": "Vodka",
"discountPercentage": 19
}
]
},
{
"eventName": "Steal of a Deal Days",
"promotionalDates": {
"startDate": {
"Year": 2024,
"Month": 9,
"Day": 21
},
"endDate": {
"Year": 2024,
"Month": 9,
"Day": 29
}
},
"discounts": [
{
"categoryName": "Organic Wine",
"discountPercentage": 19
},
{
"categoryName": "White Wine",
"discountPercentage": 20
},
{
"categoryName": "Sparkling Wine",
"discountPercentage": 19
},
{
"categoryName": "Whiskey",
"discountPercentage": 17
},
{
"categoryName": "Vodka",
"discountPercentage": 23
}
]
}
]
}Example 1 - Calculate the standard deviation of total sales
This query calculates the standard deviation of total sales across stores in the "Fourth Coffee" company by taking a random sample of 10 documents matching the filtering criteria.
db.stores.aggregate([{
$match: {
"company": "Fourth Coffee"
}
}, {
$sample: {
size: 10
}
}, {
$group: {
_id: "$company",
stdDev: {
$stdDevSamp: "$sales.totalSales"
}
}
}])This query returns the following result:
[
{
"_id": "Fourth Coffee",
"stdDev": 22040.044055209048
}
]