Group by day/month/week basis on the date range - mongodb

Question

This is in reference to this question.
This is my data set:
[
{
"rating": 4,
"ceatedAt": ISODate("2016-08-08T15:32:41.262+0000")
},
{
"rating": 3,
"createdAt": ISODate("2016-08-08T15:32:41.262+0000")
},
{
"rating": 3,
"ceatedAt": ISODate("2016-07-01T15:32:41.262+0000")
},
{
"rating": 5,
"createdAt": ISODate("2016-07-01T15:32:41.262+0000")
}
]
I want to be able to filter basis on week or month basis on the date range.
How would I do that in mongo?
This was the answer given for grouping by days.
db.collection.aggregate([
{
"$project": {
"formattedDate": {
"$dateToString": { "format": "%Y-%m-%d", "date": "$ceatedAt" }
},
"createdAtMonth": { "$month": "$ceatedAt" },
"rating": 1
}
},
{
"$group": {
"_id": "$formattedDate",
"average": { "$avg": "$rating" },
"month": { "$first": "$createdAtMonth" },
}
}
])

Answer 1

For grouping on weekly basis, run the following pipeline which mainly uses the Date Aggregation Operators to extract the date parts:
db.collection.aggregate([
{
"$project": {
"createdAtWeek": { "$week": "$createdAt" },
"createdAtMonth": { "$month": "$createdAt" },
"rating": 1
}
},
{
"$group": {
"_id": "$createdAtWeek",
"average": { "$avg": "$rating" },
"month": { "$first": "$createdAtMonth" }
}
}
])
and for monthly aggregates, interchange the $group key to use the created month field:
db.collection.aggregate([
{
"$project": {
"createdAtWeek": { "$week": "$createdAt" },
"createdAtMonth": { "$month": "$createdAt" },
"rating": 1
}
},
{
"$group": {
"_id": "$createdAtMonth",
"average": { "$avg": "$rating" },
"week": { "$first": "$createdAtWeek" }
}
}
])