$covarianceSamp
The $covarianceSamp operator returns the covariance of a sample of two numerical expressions
$covarianceSamp
The $covarianceSamp operator sorts documents on one or more fields within a partition and calculates the covariance of a sample two numerical fields within a specified document window.
Parameters
| Parameter | Description |
|---|---|
numericalExpression1 | The first numerical expression to use to calculate the covariance sample within the specified document window |
numericalExpression2 | The first numerical expression to use to calculate the covariance sample within the specified document window |
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 covariance sample between an unbounded starting document and the current document
To calculate the covariance sample for stores in the First Up Consultants company, first run a query to filter on the company, then sort the resulting stores in ascending order of their opening dates, and calculate the covariance of the sales of the sorted result set.
db.stores.aggregate(
[{
"$match": {
"company": {
"$in": [
"First Up Consultants"
]
},
"$and": [
{
"storeOpeningDate": {
"$gt": ISODate("2024-09-01T03:06:24.180Z")
}
},
{
"storeOpeningDate": {
"$lt": ISODate("2025-09-30T03:55:17.557Z")
}
}
]
}
},
{
"$setWindowFields": {
"partitionBy": "$company",
"sortBy": {
"storeOpeningDate": 1
},
"output": {
"covarianceSampForSales": {
"$covarianceSamp": [
{
"$hour": "$storeOpeningDate"
},
"$sales.revenue"
],
"window": {
"documents": [
"unbounded",
"current"
]
}
}
}
}
},
{
"$project": {
"company": 1,
"name": 1,
"sales.revenue": 1,
"storeOpeningDate": 1,
"covarianceSampForSales": 1
}
}]
)The first two results returned by this query are:
[
{
"_id": "2d315043-db26-4d18-8bb7-71ba922f00a0",
"name": "First Up Consultants | Furniture Shoppe - Wymantown",
"sales": {
"revenue": 38042
},
"company": "First Up Consultants",
"storeOpeningDate": "2024-09-02T02:00:52.592Z",
"covarianceSampForSales": 935.0972222222222
},
{
"_id": "416adb8c-7d65-40e5-af88-8659c71194ce",
"name": "First Up Consultants | Picture Frame Bazaar - South Lysanneborough",
"sales": {
"revenue": 37157
},
"company": "First Up Consultants",
"storeOpeningDate": "2024-09-02T02:39:50.269Z",
"covarianceSampForSales": 1901.1777777777777
}
]