$group stage for aggregation in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to group documents by the field 'category'.

MongoDB

db.collection.aggregate([{ $group: { _id: "$"[1] } } }])

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

Acategory

Bname

Cprice

Ddate

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the dollar sign before the field name.

Using a field name that does not exist in the documents.

The $group stage groups documents by the specified field. Here, grouping by 'category' means documents with the same category are combined.

2fill in blank

medium

Complete the code to calculate the total quantity for each product using $sum.

MongoDB

db.collection.aggregate([{ $group: { _id: "$product", totalQuantity: { $[1]: "$quantity" } } } }])

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

Asum

Bavg

Cmax

Dmin

Attempts:

3 left

💡 Hint

Common Mistakes

Using $avg instead of $sum when summing values.

Not prefixing the operator with a dollar sign.

The $sum operator adds up the values of the specified field for each group.

3fill in blank

hard

Fix the error in the $group stage to count documents per user.

MongoDB

db.collection.aggregate([{ $group: { _id: "$user", count: { $[1]: 1 } } } }])

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

Aavg

Btotal

Ccount

Dsum

Attempts:

3 left

💡 Hint

Common Mistakes

Using $count inside $group which is invalid.

Using $avg or other operators instead of $sum.

To count documents, use $sum: 1 which adds 1 for each document in the group.

4fill in blank

hard

Fill both blanks to group by 'department' and calculate the maximum salary.

MongoDB

db.collection.aggregate([{ $group: { _id: "$"[1], maxSalary: { $[2]: "$salary" } } } }])

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

Adepartment

Bsum

Cmax

Demployee

Attempts:

3 left

💡 Hint

Common Mistakes

Using $sum instead of $max when looking for maximum.

Grouping by a wrong field name.

Grouping by 'department' groups employees by their department. Using $max finds the highest salary in each group.

5fill in blank

hard

Fill all three blanks to group by 'team', calculate average age, and count members.

MongoDB

db.collection.aggregate([{ $group: { _id: "$"[1], averageAge: { $[2]: "$age" }, memberCount: { $[3]: 1 } } } }])

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

Ateam

Bavg

Csum

Ddepartment

Attempts:

3 left

💡 Hint

Common Mistakes

Using $sum instead of $avg for average calculation.

Using wrong field names for grouping.

Grouping by 'team' groups members by their team. $avg calculates the average age. $sum: 1 counts the number of members.