M101P: MongoDB for Developers - Chapter 5: Aggregation Framework

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Homework 5.1

db.posts.aggregate([{$unwind:"$comments"},{$group:{_id:"$comments.author",comments:{$sum:1}}},{$sort:{comments:-1}},{$limit:1}]){ "_id" : "Elizabet Kleine", "comments" : 503 }

Homework 5.2

db.zips.aggregate([{$group:{_id:{state:"$state",city:"$city"},pop:{$sum:"$pop"}}},{$match:{pop:{$gt:25000}}},{$group:{_id:"$_id.state",pop:{$avg:"$pop"}}}])db.zips.aggregate([{$match:{$or:[{state:"CA"},{state:"NY"}]}},{$group:{_id:{state:"$state",city:"$city"},pop:{$sum:"$pop"}}},{$match:{pop:{$gt:25000}}},{$group:{_id:null,pop:{$avg:"$pop"}}}]){ "_id" : null, "pop" : 44804.782608695656 }

Homework 5.3

db.grades.aggregate([{$unwind:"$scores"},{$match:{"scores.type":{$ne:"quiz"}}},{$group:{_id:{class:"$class_id",student:"$student_id"},score:{$avg:"$scores.score"}}},{$group:{_id:"$_id.class",score:{$avg:"$score"}}},{$sort:{score:-1}},{$limit:1}]){ "_id" : 1, "score" : 64.50642324269175 }

Homework 5.4

db.zips.aggregate([{$match:{city:/^\d/}},{$group:{_id:null,pop:{$sum:"$pop"}}}]){ "_id" : null, "pop" : 298015 }

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