05 - MongoDB Aggregation

Question 1

Syntax when using pipeline

Answer 1

collection = "tweets"
pipeline = [$stage1, $stage2, ...$stageN]
db.<COLLECTION>.aggregate( pipeline, { options } )

Question 2

$match

Answer 2

Similar to find()

Question 3

$project

Answer 3

Shape documents

Question 4

$sort

Answer 4

Like the cursor method of the same name

Question 5

Define & list

$group

LIst - 4

Answer 5

Used to aggregate field values from multiple documents
$sum
$avg
$min
$max

Question 6

$limit

Answer 6

Used to limit the amount of documents returned

Question 7

$unwind

Answer 7

Separates documents with arrays

Question 8

$out

Answer 8

Specifies an output collection

Question 9

Similar to find()

Answer 9

$match

Question 10

Shape documents

Answer 10

$project

Question 11

Like the cursor method of the same name

Answer 11

$sort

Question 12

Used to aggregate field values from multiple documents
$sum
$avg
$min
$max

Answer 12

Define & list

$group

LIst - 4

Question 13

Used to limit the amount of documents returned

Answer 13

$limit

Question 14

Separates documents with arrays

Answer 14

$unwind

Question 15

Specifies an output collection

Answer 15

$out

Question 16

Code

Count number of action movies (with $count)

Answer 16

db.moviesSmall.aggregate([{"$match" : {"category" : "action"}}, {"$count" : "movies"}])

Question 17

Find the rating of the highest rated expensive movie
(aggregate)
budget
imdb_rating

Answer 17

`db.moviesSmall.aggregate([{

“$match” : {“budget” : {“$gt” : 25}}},

{“$group” : {“_id” : “movies”,

“highest” : {“$max” : “$imdb_rating”}}}])`

Question 18

Get class with the most number of students

Answer 18

db.grades.aggregate([{"$group" : {"_id" : "$class_id", "num_students" : {"$sum" : 1}}}, {"$group" : {"_id" : 1, "most" :  { "$max" : "$num_students"}}}])

Question 19

Get class with the most number of students (sort)
aggregate
class_id
num_students

Answer 19

db.grades.aggregate([{"$group" : {"_id" : "$class_id", "num_students" : {"$sum" : 1}}}, { "$sort" : {"num_students" : -1}}, { "$limit" : 1}])