calculate the difference betwen Two values on the same document - mongodb

Question

I am new to Mongo aggregation.I want to calculate the difference betwen Two values (The last collection for each day -The first collection for each day).the data base record data every 5 mn for many ressource name.The structucture of the document is :
{
_id : ObjectId("5820511a95d447ed648b45d6"),
DeviceName : "OLT01FTV",
ResourceName : "CM MAC:00-07-11-11-39-20",
CollectionTime : ISODate("2016-11-07T09:30:00.000+01:00"),
GranularityPeriod : 5,
A : 0,
B: 17,
C: 4,
D: 21,
E: 3,
F: 0
}
A,B...F are the differrent counters.
Below, the illustration of that I'm trying to have :
result
([
{ "$match": {
"CollectionTime": {
$gte: ISODate("2016-09-05T00:00:00.000Z"),
$lt: ISODate("2016-10-07T00:00:00.000Z")
}
}},
{ "$unwind": "$u2000" },
{ "$group": {
"_id": null,
"firstUC": { "$first": "$UC" },
"lastUC": { "$last": "$UC" },
"firstSM-MISS": { "$first": "$SM-MISS" },
"lastSM-MISS": { "$last": "$SM-MISS" }
}},
{ "$project": {
"diff": {
"$divide": [
{ "$subtract": [ "$firstUC", "$lastUC" ] },
{ "$subtract": [ "$firstSM-MISS", "$lastSM-MISS" ] }
]
}
}}
])

Answer 1

This will get you the difference between the 'A' values for your above scenario. You can add the other fields if you want to get the difference for them also.
db.collection.aggregate([
{ "$match": {
"CollectionTime": {
$gte: ISODate("2016-11-01T00:00:00.000Z"),
$lt: ISODate("2016-11-30T00:00:00.000Z")
}
}},
{ "$sort": { "CollectionTime": 1 } },
{ "$group": {
"_id": null,
"firstA": { "$first": "$A" },
"lastA": { "$last": "$A" }
}},
{ "$project": {
_id: 0,
diffA: {
$subtract: [ "$lastA", "$firstA"]
}
}}
])
* EDIT *
So I'm using the following sample documents I created with the following to match your schema:
// Create 3 Documents 1 second apart
for (var i = 1; i < 4; i++) {
db.foo.insert({
DeviceName : "OLT01FTV",
ResourceName : "CM MAC:00-07-11-11-39-20",
CollectionTime : new Date(),
GranularityPeriod : 5,
A : 1*i,
B: 2*i,
C: 3*i,
D: 4*i,
E: 5*i,
F: 6*i
})
sleep(1000); // To add a delay between insertions so we can visibly see the date difference
}
This results in the following 3 documents being created:
> db.foo.find().pretty()
{
"_id" : ObjectId("582b1a6ced19a7334a5dee31"),
"DeviceName" : "OLT01FTV",
"ResourceName" : "CM MAC:00-07-11-11-39-20",
"CollectionTime" : ISODate("2016-11-15T14:23:40.934Z"),
"GranularityPeriod" : 5,
"A" : 1,
"B" : 2,
"C" : 3,
"D" : 4,
"E" : 5,
"F" : 6
}
{
"_id" : ObjectId("582b1a6ded19a7334a5dee32"),
"DeviceName" : "OLT01FTV",
"ResourceName" : "CM MAC:00-07-11-11-39-20",
"CollectionTime" : ISODate("2016-11-15T14:23:41.936Z"),
"GranularityPeriod" : 5,
"A" : 2,
"B" : 4,
"C" : 6,
"D" : 8,
"E" : 10,
"F" : 12
}
{
"_id" : ObjectId("582b1a6eed19a7334a5dee33"),
"DeviceName" : "OLT01FTV",
"ResourceName" : "CM MAC:00-07-11-11-39-20",
"CollectionTime" : ISODate("2016-11-15T14:23:42.939Z"),
"GranularityPeriod" : 5,
"A" : 3,
"B" : 6,
"C" : 9,
"D" : 12,
"E" : 15,
"F" : 18
}
The first step of the aggregation pipeline will match on all documents between the date range - which I set to beginning of November... so no worry there, then the sorting will sort by collection time:
After the grouping we have one document with the firstA and lastA value:
{ "_id" : null, "firstA" : 1, "lastA" : 3 }
And finally - perform the subtract in the projection and hide the ID field:
{ "diffA" : 2 }