MongoDB group with project - mongodb

Question

I am trying to select maximum value of a field along with the time it occured.
db.temperaterdata.aggregate([
{
$match: {
$and: [
{ "organization_id": 37 },
{
"resulttime":{
$gte:'2020-05-01 00:00',
$lte:'2020-05-29 23:59'
}
}
]
}
},
{
"$group": {
"_id": "$userid",
maxTemperature: { $max: "$temperature"},
minTemperature: { $min: "$temperature"}
}
},
{
"$project": {
"resulttime":1,
maxTemperature:1,
minTemperature:1
}
}
]);
However, the time for which the maximum/minimum temperature has occurred it's not showing up. The result coming is like this:
{ "_id" : 233, "maxTemperature" : 100.67, "minTemperature" : 98.56 }
{ "_id" : 256, "maxTemperature" : 100.67, "minTemperature" : 98.56 }
{ "_id" : 263, "maxTemperature" : 100.67, "minTemperature" : 98.56 }
Any help will be much appreciated.

Answer 1

You need to order by userId + temperature and take max / min documents with $first / $last operators.
Try the query below:
db.temperaterdata.aggregate([
{
"$match": {
"organization_id": 37,
"resulttime": {
"$gte": "2020-05-01 00:00",
"$lte": "2020-05-29 23:59"
}
}
},
{
"$sort": {
"userid": 1,
"temperature": 1
}
},
{
"$group": {
"_id": "$userid",
"maxTemperature": {
"$last": "$$ROOT"
},
"minTemperature": {
"$first": "$$ROOT"
}
}
},
{
"$project": {
"maxresulttime": "$maxTemperature.resulttime",
"minresulttime": "$minTemperature.resulttime",
"maxTemperature": "$maxTemperature.temperature",
"minTemperature": "$minTemperature.temperature"
}
}
])
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