$covariancePop

运算符 $covariancePop 对分区中的一个或多个字段的文档进行排序，并计算指定文档窗口中两个数值字段的协变。

Syntax

{
  $covariancePop: [ < numericalExpression1 > , < numericalExpression2 > ]
}

参数

例子

请考虑商店集合中的这个示例文档。

{
    "_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
                }
            ]
        }
    ]
}

示例 1 - 计算销售量中的协方差

若要获取First Up Consultants公司各个商店总销售额的协方差，请先运行查询筛选公司名称，然后按上次更新时间戳升序对结果文档进行排序，并计算排序结果集中的首个文档与当前文档之间的协方差。

db.stores.aggregate(
    [{
            "$match": {
                "company": {
                    "$in": [
                        "First Up Consultants"
                    ]
                }
            }
        },
        {
            "$setWindowFields": {
                "partitionBy": "$company",
                "sortBy": {
                    "lastUpdated": 1
                },
                "output": {
                    "covariancePopForSales": {
                        "$covariancePop": [{
                                "$hour": "$lastUpdated"
                            },
                            "$sales.totalSales"
                        ],
                        "window": {
                            "documents": [
                                "unbounded",
                                "current"
                            ]
                        }
                    }
                }
            }
        },
        {
            "$project": {
                "company": 1,
                "name": 1,
                "sales.totalSales": 1,
                "lastUpdated": 1,
                "covariancePopForSales": 1
            }
        }
    ]
)

此查询返回的前两个结果为：

[
    {
        "_id": "2cf3f885-9962-4b67-a172-aa9039e9ae2f",
        "sales": {},
        "company": "First Up Consultants",
        "lastUpdated": "2025-06-11T10:48:01.291Z",
        "name": "First Up Consultants | Bed and Bath Center - South Amir",
        "covariancePopForSales": null
    },
    {
        "_id": "8e7a259b-f7d6-4ec5-a521-3bed53adc587",
        "name": "First Up Consultants | Drone Stop - Lake Joana",
        "sales": {},
        "company": "First Up Consultants",
        "lastUpdated": {
            "t": 1727827539,
            "i": 1
        },
        "covariancePopForSales": null
    }
]

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