MongoDB Aggregation based on userID and time period - mongodb

Question

I would like to achieve something like
{ _id: "A", count: 2 }
{ _id: "B", count: 1 }
from
{ userId: "A", timeStamp: "12:30PM" } <- start of 5 min interval A: 1
{ userId: "B", timeStamp: "12:30PM" } <- start of 5 min interval B: 1
{ userId: "B", timeStamp: "12:31PM" } <- ignored
{ userId: "A", timeStamp: "12:32PM" } <- ignored
{ userId: "B", timeStamp: "12:33PM" } <- ignored
{ userId: "A", timeStamp: "12:37PM" } <- start of next 5 min A : 2
where it groups based on userId and then after userId is group, the count is triggered every 5 mins.
For example: Within any 5 min period, starting at say midnight, an unlimited number of collections can have a timeStamp from 00:00 to 00:05 but would only be counted as 1 hit.
Hopefully I am explaining this clearly.
I'm able to group by userId and get the count in general but setting a condition of the count seems to be tricky.

Answer 1

You can try $bucket and $addToSet - the drawback is that you have to specify all the ranges manually:
db.col.aggregate([
{
$bucket: {
groupBy: "$timeStamp",
boundaries: [ "12:30PM", "12:35PM", "12:40PM", "12:45PM", "12:50PM", "12:55PM", "13:00PM" ],
output: {
"users" : { $addToSet: "$userId" }
}
}
},
{
$unwind: "$users"
},
{
$group: { _id: "$users", count: { $sum: 1 } }
}
])

Answer 2

Micki's solution is better if you have mongo 3.6.
If you have mongo 3.4 you can use $switch.
Obviously you would need to add all the cases in the day.
db.getCollection('user_timestamps').aggregate(
{
$group: {
_id: '$userId',
timeStamp: {$push: '$timeStamp'}
}
},
{
$project: {
timeStamps: {
$map: {
input: '$timeStamp',
as: 'timeStamp',
in: {
$switch: {
branches: [
{
case: {
$and: [
{$gte: ['$$timeStamp', '12:30PM']},
{$lt: ['$$timeStamp', '12:35PM']}
]
},
then: 1
},
{
case: {
$and: [
{$gte: ['$$timeStamp', '12:35PM']},
{$lt: ['$$timeStamp', '12:40PM']}
]
},
then: 2
}
],
default: 0
}
}
}
}
}
},
{
$unwind: '$timeStamps'
},
{
$group: {
_id: '$_id',
count: {
$addToSet: '$timeStamps'
}
}
},
{
$project: {
_id: true,
count: {$size: '$count'}
}
}
)
If you don't have mongo 3.4 you can replace the $switch with
cond: [
{
$and: [
{$gte: ['$$timeStamp', '12:30PM']},
{$lt: ['$$timeStamp', '12:35PM']}
]
},
1,
{
cond: [
{
$and: [
{$gte: ['$$timeStamp', '12:35PM']},
{$lt: ['$$timeStamp', '12:40PM']}
]
},
2,
0
]
}
]