我想计算一个名为management_fee的对象的lower_limit，为了计算这个变量，我需要获得management_fee的平均值，然后我需要获得标准差。计算完两个变量后，我可以减去平均值减去标准差。
这是我当前正在开发的 JSO 示例:
{
"_id": "5d44ef5ea366bfcdc21",
"user": "5d2f594faa4182c47c",
"management_fee": 399,
"cancellation_date": "2017-05-02T00:00:00.000Z",
"country": "USA",
"state": "Texas",
"__v": 0
},
{
"_id": "5d44ef5ea366bfcdc22",
"user": "5d2f594faa4182c42c",
"management_fee": 599,
"cancellation_date": "2017-08-09T00:00:00.000Z",
"country": "USA",
"state": "Texas",
"__v": 0
},
{
"_id": "5d44ef5ea366bfcdc23",
"user": "5d2f594faa4182c48c",
"management_fee": 700,
"cancellation_date": "2017-08-09T00:00:00.000Z",
"country": "USA",
"state": "New York",
"__v": 0
}
在下面的代码中，我想按年份对 lower_limit 进行分组，然后通过计算 management_fee 的平均值和偏差标准来计算，这样我就可以将两者相减。
router.get('/random_test_10', auth, async (req, res) => {
try {
const model_CancellationKPI = await CancellationKPI.aggregate([
{
$group: {
_id: {year:{$year: "$cancellation_date"}},
lower_limit: {$subtract:[ {std:{$stdDevSamp: "$management_fee"}, avr:{$avg:"$management_fee"}}]},
}
}
])
res.json(model_CancellationKPI);
} catch (err) {
console.error(err.message);
res.status(500).send('Server Error')
}
});
下面提供的答案效果很好。但是，现在我想在同一输出中添加总计和平均值，但我收到 null 和 0。你知道为什么吗？
这是我的代码:
router.get('/random_test_11', auth, async (req, res) => {
try {
const model_CancellationKPI = await CancellationKPI.aggregate([{
$group: {
_id: { year: { $year: "$cancellation_date" } },
std: { $stdDevSamp: '$management_fee' }, avg: { $avg: '$management_fee' }
}},
{ $project: { year: '$_id.year', _id: 0,
result: { $subtract: ['$avg', '$std'] }, average: {$avg: '$management_fee'},
total: {$sum: '$management_fee}'}
} }])
res.json(model_CancellationKPI);
} catch (err) {
console.error(err.message);
res.status(500).send('Server Error')
}
});
这是输出:
[
{
"year": 2017,
"result": 388.90493206697874,
"average": null,
"total": 0
},
{
"year": 2019,
"result": 88.03232361610253,
"average": null,
"total": 0
},
{
"year": 2018,
"result": 367.4573075192308,
"average": null,
"total": 0
}
]
最佳答案
请尝试这个:
db.getCollection('CancellationKPI').aggregate([{
$group: {
_id: { year: { $year: "$cancellation_date" } }, std: { $stdDevSamp: '$management_fee' },total :{$sum :'$management_fee'}, average: { $avg: '$management_fee' }
}
}, { $project: { year: '$_id.year', _id: 0, average: 1, total: 1, result: { $subtract: ['$average', '$std'] } } }])
关于node.js - 如何在 mongoDB 中减去 2 个操作？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/57468247/