Created
December 3, 2012 02:53
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m101 - Mongo HW 5
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| db.posts.aggregate( [ { $project : { 'comments.author': 1 } }, { $unwind : "$comments" }, { $group : { _id : { comments : "$comments" }, n : { $sum : 1 } } }, { $sort: {"n": -1} } ] ) |
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| db.zips.aggregate([ | |
| { | |
| "$match": { | |
| state: {"$in": ["CA", "NY"]} | |
| } | |
| }, | |
| { | |
| "$group": { | |
| "_id": {"state": "$state", "city": "$city"}, | |
| tPop: {"$sum": "$pop" } | |
| } | |
| }, | |
| { | |
| "$match": { | |
| "tPop": { "$gt": 25000 } | |
| } | |
| }, | |
| { | |
| "$group": { | |
| _id: "$state", | |
| average: {"$avg": "$tPop"} | |
| } | |
| } | |
| ]) |
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| db.grades.aggregate([ | |
| { | |
| "$match": { | |
| "scores.type": { | |
| "$in": ["exam", "homework"] | |
| } | |
| } | |
| }, | |
| { | |
| "$unwind": "$scores" | |
| }, | |
| { | |
| "$group": { | |
| _id: {"student_id": "$student_id", "class_id": "$class_id"}, | |
| sGPA: {"$avg": "$scores.score"} | |
| } | |
| }, | |
| { | |
| "$group": { | |
| _id: {"class_id": "$_id.class_id"}, | |
| cGPA: {"$avg": "$sGPA"} | |
| } | |
| }, | |
| { | |
| "$sort": { | |
| cGPA: -1 | |
| } | |
| } | |
| ]) |
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| db.zips.aggregate([ | |
| { | |
| "$project": { | |
| "fc": {"$substr": ["$city", 0, 1]}, | |
| "city": 1, | |
| "pop": 1 | |
| } | |
| }, | |
| { | |
| "$match": { | |
| "fc": {"$in": ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"]} | |
| } | |
| }, | |
| { | |
| "$group": { | |
| _id: null, | |
| pop: {"$sum": "$pop"} | |
| } | |
| } | |
| ]) |
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@marcoberri, I know that it's been two year since your comment, but actually it is not important which _id to use in the last group, if you write _id: null the answer will be the same