$addToSet accumulator for unique arrays in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to use $addToSet to add unique values to the array.

MongoDB

{ $group: { _id: "$category", items: { [1]: "$item" } } }

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

A$sum

B$push

C$addToSet

D$avg

Attempts:

3 left

💡 Hint

Common Mistakes

Using $push instead of $addToSet, which allows duplicates.

Using $sum or $avg which are for numeric calculations, not arrays.

The $addToSet accumulator adds unique values to an array, avoiding duplicates.

2fill in blank

medium

Complete the aggregation stage to group by "type" and collect unique "tags" using $addToSet.

MongoDB

{ $group: { _id: "$type", uniqueTags: { [1]: "$tags" } } }

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

A$push

B$max

C$first

D$addToSet

Attempts:

3 left

💡 Hint

Common Mistakes

Using $push which does not remove duplicates.

Using $first or $max which return single values, not arrays.

$addToSet collects unique values from the "tags" field into an array.

3fill in blank

hard

Fix the error in the aggregation pipeline to correctly use $addToSet for unique "colors".

MongoDB

{ $group: { _id: "$brand", colors: { [1]: "$colors" } } }

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

A$addToSet

B$avg

C$sum

D$push

Attempts:

3 left

💡 Hint

Common Mistakes

Using $push instead of $addToSet.

Using numeric accumulators like $sum or $avg for arrays.

Only $addToSet correctly accumulates unique values in an array.

4fill in blank

hard

Fill both blanks to group by "department" and collect unique "employees" using $addToSet.

MongoDB

{ $group: { _id: "$department", [1]: { [2]: "$employee" } } }

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

Astaff

B$push

C$addToSet

Dmembers

Attempts:

3 left

💡 Hint

Common Mistakes

Using $push instead of $addToSet.

Using field names like "members" without matching the code.

The field name can be any valid name like "staff"; $addToSet collects unique employees.

5fill in blank

hard

Fill both blanks to group by "category", collect unique "products" with $addToSet, and name the array "uniqueProducts".

MongoDB

{ $group: { _id: "$category", [1]: { [2]: "$product" } } }

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

AuniqueProducts

B$addToSet

C$push

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using $push which allows duplicates.

Confusing field names or accumulator names.

The field name is "uniqueProducts", the accumulator is $addToSet, and "items" is a distractor option not used here.