[{"date":ISODate("2021-05-31T00:00:00.000Z"),"key":1},{"date":ISODate("2021-05-30T00:00:00.000Z"),"key":2},{"date":ISODate("2021-05-22T00:00:00.000Z"),"key":2},{"date":ISODate("2021-05-23T00:00:00.000Z"),"key":2},{"date":ISODate("2021-05-24T00:00:00.000Z"),"key":2},{"date":ISODate("2021-05-25T00:00:00.000Z"),"key":2},{"date":ISODate("2021-05-26T00:00:00.000Z"),"key":2},{"date":ISODate("2021-05-27T00:00:00.000Z"),"key":2},{"date":ISODate("2021-05-28T00:00:00.000Z"),"key":2},]

db.collection.aggregate([{"$group":{"_id":{"week":{"$week":"$date"},"year":{"$year":"$date"},}},},{"$project":{"_id":{"startDate":{"$dateToString":{"date":{"$dateFromParts":{"isoWeekYear":"$_id.year","isoWeek":"$_id.week"}},"format":"%Y-%m-%d",},},"endDate":{"$dateToString":{"date":{"$add":[{"$dateFromParts":{"isoWeekYear":"$_id.year","isoWeek":"$_id.week"}},518400000,],},"format":"%Y-%m-%d",},},},},},])