Mongodb Muliple averages based on a different column - mongodb

Question

Using mongodb aggregate, is there a way to have the query return Weight average on all Scale , an average of Scale 1 , an average of Scale 2 all all returned in the same query?
This is an example of an entry in my data set
{
"Profile" : "P1",
"AvgWeight" : 639,
"Time" : "2017-04-14T05:17:42.000Z",
"Scale" : 1,
"Weight" : 1504,
"Target" : 680
}
My query that I am currently running that is averaging the weight accrost all scales ( Might not help, but better to have more info )
[{
"$match": {
"Time": {
"$gt": moment(start).format("YYYY-MM-DD HH:mm:ss"),
"$lt": moment(end).format("YYYY-MM-DD HH:mm:ss")
}
}
},
{
"$group": {
"_id": {
"hour": {
"$hour": "$Time"
},
"day": {
"$dayOfYear": "$Time"
},
"interval": {
"$add": [{
"$multiply": [{
"$minute": "$Time"
}]
},
{
"$multiply": [{
"$hour": "$Time"
},
100
]
},
{
"$multiply": [{
"$dayOfYear": "$Time"
},
10000
]
},
{
"$multiply": [{
"$year": "$Time"
},
10000000
]
}
]
}
},
"time": {
"$first": "$Time"
},
"avgW": {
"$avg": "$AvgWeight"
},
"avgWe": {
"$avg": "$Weight"
},
"avgTarget": {
"$avg": "$Target"
}
}
}, {
"$sort": {
"Time": -1
}
}
]
Adding Expected Response SOmething like
[
{
"_id : {"hour":1,"day":105,"interval":20971050122},
"time":"2017-04-15T01:22:58.000Z",
"avgW":646,
"avgWe":1577,
"avgTarget":680 ,
"Scale1" : 100 ,
"Scale2" : 120
} ,
{ "_id":{"hour":1,"day":105,"interval":20771050122},
"time":"2017-04-15T01:22:55.000Z",
"avgW":646,
"avgWe":1335,
"avgTarget":680 ,
"Scale1" : 100 ,
"Scale2" : 120 }
]
But if it is a little different I can handle it, as long all the scales are in the same parent object ( it would be to cpu intensive to post process them to link up the matching groups )

Answer 1

You can split the first group into two groups.
First group to calculate weight avg for all scales and second group to do rest of avgs.
Something like:
[{
"$match": {
"Time": {
"$gt": moment(start).format("YYYY-MM-DD HH:mm:ss"),
"$lt": moment(end).format("YYYY-MM-DD HH:mm:ss")
}
}
}, {
"$group": {
"_id": {
"scale": "$Scale",
"hour": {
"$hour": "$Time"
},
"day": {
"$dayOfYear": "$Time"
},
"interval": {
"$add": [{
"$multiply": [{
"$minute": "$Time"
}]
},
{
"$multiply": [{
"$hour": "$Time"
},
100
]
},
{
"$multiply": [{
"$dayOfYear": "$Time"
},
10000
]
},
{
"$multiply": [{
"$year": "$Time"
},
10000000
]
}
]
}
},
"time": {
"$first": "$Time"
},
"scaleAvg: {
"$avg": "$Weight"
}
}
}, {
"$group": {
"_id": {
"hour": "$_id.hour",
"day": "$_id.day",
"interval": "$_id.interval"
},
"time": {
"$first": "$time"
},
"avgW": {
"$avg": "$AvgWeight"
},
"avgWe": {
"$avg": "$Weight"
},
"avgTarget": {
"$avg": "$Target"
},
"scaleAvgs": {
"$push": {
"scale": "$_id.scale",
"scaleAvg": "$scaleAvg"
}
}
}
}, {
"$sort": {
"time": -1
}
}]