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

Question

This is in reference to this question.

This is my data set:

[
  {
    \"rating\": 4,
    \"ceatedAt\": ISODate(\"2016-08-08T15:32:41.262+0000\")
  },
  {         


        

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" }
         }
    }
])