Using Mongo to calculate sum in Aggregator pipeline - mongodb

Question

I have a timeseries data in mongodb and I want to calculate the sum per day between two given dates of every sensor after I have calculated the difference between the max and min reading of the day by the sensor, using the below query
db.ts_events.aggregate([
{ $match: {
"metadata.assetCode": { $in: [
"h"
]
},
"timestamp": { $gte: ISODate("2022-07-01T02:39:02.000+0000"), $lte: ISODate("2022-07-01T06:30:00.000+0000")
}
}
},
{
$project: {
date: {
$dateToParts: { date: "$timestamp"
}
},
activeEnergy: 1,
"metadata.meterId": 1,
}
},
{
$group: {
_id: {
date: {
year: "$date.year",
month: "$date.month",
day: "$date.day"
},
meter: "$metadata.meterId",
},
maxValue: { $max: "$activeEnergy"
},
minValue: { $min: "$activeEnergy"
},
}
},
{
$addFields: {
differnce: { $subtract: [
"$maxValue",
"$minValue"
]
},
}
},
])
I get the following output
{
"_id" : {
"date" : {
"year" : NumberInt(2022),
"month" : NumberInt(7),
"day" : NumberInt(1)
},
"meter" : "B"
},
"maxValue" : 1979.78,
"minValue" : 1979.77,
"differnce" : 0.009999999999990905
}
{
"_id" : {
"date" : {
"year" : NumberInt(2022),
"month" : NumberInt(7),
"day" : NumberInt(1)
},
"meter" : "A"
},
"maxValue" : 7108.01,
"minValue" : 7098.18,
"differnce" : 9.829999999999927
}
I want to calculate the sum of both meter difference how can I do that?
Apart from this one more problem I am facing which I am putting forward in this edited version, as you can see date is in ISODate format but I will be getting a unix epoch format,
I tried to tweak the query but it is not working
db.ts_events.aggregate([
{
$project: {
date: {
$dateToParts: {
date: "$timestamp"
}
},
activeEnergy: 1,
"metadata.meterId": 1,
"metadata.assetCode": 1,
"timestamp": 1,
startDate: {
$toDate: 1656686342000
},
endDate: {
$toDate: 1656700200000
}
}
},
{
$match: {
"metadata.assetCode": {
$in: [
"h"
]
},
"timestamp": {
$gte: "$startDate", $lte: "$endDate"
}
}
},
{
$group: {
_id: {
date: {
year: "$date.year",
month: "$date.month",
day: "$date.day"
},
meter: "$metadata.meterId",
},
maxValue: {
$max: "$activeEnergy"
},
minValue: {
$min: "$activeEnergy"
},
}
},
{
$addFields: {
differnce: {
$subtract: [
"$maxValue",
"$minValue"
]
},
}
},
{
$group: {
_id: "$_id.date", res: {
$push: '$$ROOT'
}, differnceSum: {
$sum: '$differnce'
}
}
}
])
Can you help me solve the problem?

Answer 1

One option is to add one more step like this (depending on your expected output format):
This step will group together your separate documents, into one document, which will allow you to sum their values together. Be careful when grouping, since now it is a one big document and a document has a size limit.
We use $$ROOT to keep the original document structure (here inside a new array)
{$group: {_id: 0, res: {$push: '$$ROOT'}, differnceSum: {$sum: $differnce'}}}