$count accumulator in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to count all documents in the collection.

MongoDB

db.collection.aggregate([{ $group: { _id: null, total: { [1]: {} } } }])

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

A$count

B$sum

C$avg

D$max

Attempts:

3 left

💡 Hint

Common Mistakes

Using $sum instead of $count to count documents.

Using $avg or $max which do not count documents.

The $count accumulator counts the number of documents in the group.

2fill in blank

medium

Complete the code to count documents grouped by category.

MongoDB

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

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

A$count

B$sum

C$min

D$max

Attempts:

3 left

💡 Hint

Common Mistakes

Using $sum: 1 instead of $count.

Using $min or $max which do not count documents.

Use $count to count documents per group by category.

3fill in blank

hard

Fix the error in the aggregation to count documents by status.

MongoDB

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

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

A$avg

B$sum

C$count

D$max

Attempts:

3 left

💡 Hint

Common Mistakes

Using $sum: 1 instead of $count: {}.

Passing a value to $count which expects an empty object.

The $count accumulator does not take a value; $sum: 1 counts documents but $count is the correct accumulator here.

4fill in blank

hard

Fill both blanks to count documents grouped by type and filter groups with count greater than 5.

MongoDB

db.collection.aggregate([
  { $group: { _id: "$type", count: { [1]: {} } } },
  { $match: { count: { [2]: 5 } } }
])

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

A$count

B$gt

C$gte

D$sum

Attempts:

3 left

💡 Hint

Common Mistakes

Using $sum instead of $count in $group.

Using $gte instead of $gt for filtering.

Use $count to count documents per type and $gt to filter counts greater than 5.

5fill in blank

hard

Fill all three blanks to count documents by category, filter counts greater than 10, and sort descending by count.

MongoDB

db.collection.aggregate([
  { $group: { _id: [1], count: { [2]: {} } } },
  { $match: { count: { [3]: 10 } } },
  { $sort: { count: -1 } }
])

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

A"$category"

B$count

C$gt

D$sum

Attempts:

3 left

💡 Hint

Common Mistakes

Using $sum instead of $count.

Using $gte instead of $gt.

Not quoting the field name in _id.

Group by "$category", count documents with $count, filter counts greater than 10 with $gt.