$avg accumulator in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate the average score from the scores collection.

MongoDB

db.scores.aggregate([{ $group: { _id: null, averageScore: { $[1]: "$score" } } }])

Drag options to blanks, or click blank then click option'

Aavg

Bsum

Cmax

Dmin

Attempts:

3 left

💡 Hint

Common Mistakes

Using $sum instead of $avg.

Using $max or $min which find maximum or minimum values.

The $avg accumulator calculates the average value of the specified field.

2fill in blank

medium

Complete the code to calculate the average price for each product category.

MongoDB

db.products.aggregate([{ $group: { _id: "$category", avgPrice: { $[1]: "$price" } } }])

Drag options to blanks, or click blank then click option'

Asum

Bavg

Ccount

Dfirst

Attempts:

3 left

💡 Hint

Common Mistakes

Using $sum which adds values instead of averaging.

Using $count which counts documents, not averages.

The $avg accumulator calculates the average price per category.

3fill in blank

hard

Fix the error in the aggregation to correctly compute the average rating.

MongoDB

db.reviews.aggregate([{ $group: { _id: "$productId", averageRating: { $[1]: "$rating" } } }])

Drag options to blanks, or click blank then click option'

Aavg

Bsum

Cmax

Dmin

Attempts:

3 left

💡 Hint

Common Mistakes

Missing the dollar sign before the field name.

Using $sum instead of $avg.

The field name must be prefixed with a dollar sign inside $avg. Use "$rating" to refer to the field.

4fill in blank

hard

Fill both blanks to calculate the average age of users grouped by city.

MongoDB

db.users.aggregate([{ $group: { _id: "$city", [1]: { $avg: [2] } } }])

Drag options to blanks, or click blank then click option'

AaverageAge

B"$age"

C"age"

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using the field name without a dollar sign.

Using a wrong output field name like 'count'.

The first blank is the name of the output field, here averageAge. The second blank is the field to average, which must be "$age" with a dollar sign.

5fill in blank

hard

Fill all three blanks to compute the average score for each team and label the output field as 'teamAverage'.

MongoDB

db.scores.aggregate([{ $group: { _id: [1], [2]: { $[3]: "$score" } } }])

Drag options to blanks, or click blank then click option'

A"$team"

BteamAverage

Cavg

D"team"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the dollar sign in the group key.

Using $sum or other accumulators instead of $avg.

Naming the output field incorrectly.

The group key is the team field, so "$team". The output field is named teamAverage. The accumulator is $avg to calculate the average.