Is it possible to group (aggregate) objects with dates into incremental intervals in MongoDB? - mongodb

Question

I am currently trying to create an aggregation pipeline in MongoDB to group the items into incremental time intervals, but I only succeeded in grouping them in disjoint time intervals so far.
Sample data:
{
"eventID": "abc",
"date": ISODate("2020-11-05T12:05:11.790Z"),
...........
},
{
"eventID": "xyz",
"date": ISODate("2020-11-05T12:12:11.790Z"),
...........
},
{
"eventID": "klm",
"date": ISODate("2020-11-05T12:28:11.790Z"),
...........
}
Current solution:
$group: {
"_id": {
"year": { $year: "$date" },
"dayOfYear": { $dayOfYear: "$date" },
"hour": { $hour: "$date" },
"interval": {
"$subtract": [
{ "$minute": "$date" },
{ "$mod": [{ "$minute": "$date"}, 10 ] }
]
}
},
"grouped_data": { "$push": { "eventID": "$eventID", "date": "$date" },
"count": { $sum: 1 } }
}
Which returns the data grouped in 10 minutes intervals but those are disjoint intervals (time windows of 10minutes that do not intersect).
Eg:
{
"_id": {
"year": 2020,
"dayOfYear": "314",
"hour": 12,
"interval": 0, // = interval beginning at minute 0 of 12th hour of the day
},
"grouped_data": [{ "eventID": "abc", "date": ISODate("2020-11-05T12:05:11.790Z" }],
"count": 1
},
{
"_id": {
"year": 2020,
"dayOfYear": "314",
"hour": 12,
"interval": 10, // = beginning at minute 10
},
"grouped_data": [{ "eventID": "xyz", "date": ISODate("2020-11-05T12:12:11.790Z") }],
"count": 1
},
{
"_id": {
"year": 2020,
"dayOfYear": "314",
"hour": 12,
"interval": 20, // = beginning at minute 20
},
"grouped_data": [{ "eventID": "klm", "date": ISODate("2020-11-05T12:28:11.790Z") }],
"count": 1
}
What I am actually looking for is grouping them in 10 minutes(or whatever is needed) incremental intervals. Eg: 0-9, 1-10, 2-11, etc. instead of 0-9, 10-19, 20-29 etc.
Edit:
The end goal here is to check if a count threshold is surpassed on a interval length defined by the user.
If user asks "Are there more than 2 events on a 10minute time window?", based on the sample data above and my current solution, the condition is not met. (1 event in 0-9 interval, and 1 event in 10-19). With incremental intervals I should be able to find that there are indeed 2 events in 10 minutes, but in the time interval 5-14. Eg:
{
"_id": {
*whatever logic for grouping in 10minutes window*
},
"grouped_data": [
{ "eventID": "abc", "date": ISODate("2020-11-05T12:05:11.790Z") },
{ "eventID": "xyz", "date": ISODate("2020-11-05T12:12:11.790Z") }],
"count": 2
},
{
"_id": {
*whatever logic for grouping in 10minutes window*
},
"grouped_data": [
{ "eventID": "klm", "date": ISODate("2020-11-05T12:28:11.790Z") }]
"count": 1
},

Answer 1

For me it is not clear which output you like to get, but this aggregation pipeline makes the sliding-window group:
db.collection.aggregate([
{
$group: {
_id: null,
data: { $push: "$$ROOT" },
min_date: { $min: "$date" },
max_date: { $max: "$date" }
}
},
{
$addFields: {
interval: {
$range: [
{ $toInt: { $divide: [{ $toLong: "$min_date" }, 1000] } },
{ $toInt: { $divide: [{ $toLong: "$max_date" }, 1000] } },
10 * 60]
}
}
},
{
$set: {
interval: {
$map: {
input: "$interval",
in: { $toDate: { $multiply: ["$$this", 1000] } }
}
}
}
},
{ $unwind: "$interval" },
{
$project: {
grouped_data: {
$filter: {
input: "$data",
cond: {
$and: [
{ $gte: ["$$this.date", "$interval"] },
{ $lt: ["$$this.date", { $add: ["$interval", 1000 * 60 * 10] }] },
]
}
}
},
interval: 1
}
}
])
Boundaries are given by input data, however can also use fixes dates:
db.collection.aggregate([
{ $group: { _id: null, data: { $push: "$$ROOT" } } },
{
$addFields: {
interval: {
$range: [
{ $toInt: { $divide: [{ $toLong: ISODate("2020-01-01T00:00:00Z") }, 1000] } },
{ $toInt: { $divide: [{ $toLong: ISODate("2020-12-31T23:59:59Z") }, 1000] } },
10 * 60]
}
}
},
{
$set: {
interval: {
$map: {
input: "$interval",
in: { $toDate: { $multiply: ["$$this", 1000] } }
}
}
}
},
{ $unwind: "$interval" },
{
$project: {
grouped_data: {
$filter: {
input: "$data",
cond: {
$and: [
{ $gte: ["$$this.date", "$interval"] },
{ $lt: ["$$this.date", { $add: ["$interval", 1000 * 60 * 10] }] },
]
}
}
},
interval: 1
}
}
])

Answer 2

I will try to answer my own question, maybe it will help other people on the internet. The solution I came up with is based on the answer of #Wernfried (thanks!).
db.getCollection("events_en").aggregate([
{
$match: { eventID: "XYZ" }
},
{
$group: {
_id: null,
events: { $push: "$$ROOT" },
limit: { $push: { $toDate: { $add: [{ $toLong: "$date" }, 1000 * 60 * 10] } } }
}
},
{ $unwind: "$limit" },
{
$project: {
events: {
$filter: {
input: "$events",
cond: {
$and: [
{ $lt: ["$$this.date", "$limit"] },
{ $gte: ["$$this.date", { $subtract: ["$limit", 1000 * 60 * 10] }] },
]
}
}
},
limit: 1,
}
},
{
$addFields: {
count: {
$size: "$events"
}
}
}
])
This will create a limit for each event, based on its date + 10 minutes (or whatever). And afterwards it filters the events (which are now duplicated for each of the limit using $unwind: "$limit"), based on that limit. The result is something like this:
{
"_id" : null,
"limit" : ISODate("2020-11-05T12:28:27.000+0000"),
"events" : [
{
"_id" : 13,
"eventID" : "XYZ",
"date" : ISODate("2020-11-05T12:18:27.000+0000")
},
{
"_id" : 63,
"eventID" : "XYZ",
"date" : ISODate("2020-11-05T12:19:55.000+0000")
},
............................
{
"_id" : 90,
"eventID" : "XYZ",
"date" : ISODate("2020-11-05T12:27:57.000+0000")
}
],
"count" : 5
}
{
"_id" : null,
"limit" : ISODate("2020-11-05T12:29:55.000+0000"),
"events" : [
{
"_id" : 63,
"eventID" : "XYZ",
"date" : ISODate("2020-11-05T12:19:55.000+0000")
},
{
"_id" : 90,
"eventID" : "XYZ",
"date" : ISODate("2020-11-05T12:27:57.000+0000")
},
{
"_id" : 97,
"eventID" : "XYZ",
"date" : ISODate("2020-11-05T12:29:36.000+0000")
}
],
"count" : 3
}
As you can see, looking at the limit of each group and at the dates of the events in each group, these intervals are now incremental, not disjoint. (event X is found in multiple groups, as long as it doesnt exceeds the time interval of 10minutes)