适用对象：
MongoDB vCore
运算符 $abs 返回数字的绝对值。 它会从数字中删除任何负号，使其为正数。
语法
运算符的 $isArray 语法如下所示：
{ $abs: <number> }
参数
| DESCRIPTION | |
|---|---|
<number> |
解析为数字的任何有效表达式。 如果表达式解析为 null 或引用缺失字段，$abs返回 null。 |
示例：
让我们了解数据集中示例数据的 stores 使用情况。
db.stores.aggregate([
{ $match: { "_id": "40d6f4d7-50cd-4929-9a07-0a7a133c2e74" } },
{
$project: {
name: 1,
"salesByCategory": {
$map: {
input: "$sales.salesByCategory",
as: "category",
in: {
categoryName: "$$category.categoryName",
totalSales: "$$category.totalSales",
differenceFromAverage: {
$abs: {
$subtract: [
"$$category.totalSales",
{ $avg: "$sales.salesByCategory.totalSales" }
]
}
}
}
}
}
}
}
])
这将生成输出，显示每个类别的销售额与平均销售额之间的绝对差异：
{
"_id": "40d6f4d7-50cd-4929-9a07-0a7a133c2e74",
"name": "Proseware, Inc. | Home Entertainment Hub - East Linwoodbury",
"salesByCategory": [
{
"categoryName": "Sound Bars",
"totalSales": 2120,
"differenceFromAverage": 28252.8
},
{
"categoryName": "Home Theater Projectors",
"totalSales": 45004,
"differenceFromAverage": 14631.2
},
{
"categoryName": "Game Controllers",
"totalSales": 43522,
"differenceFromAverage": 13149.2
},
{
"categoryName": "Remote Controls",
"totalSales": 28946,
"differenceFromAverage": 1426.8
},
{
"categoryName": "VR Games",
"totalSales": 32272,
"differenceFromAverage": 1899.2
}
]
}