$push accumulator for building arrays in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to use $push to add values to an array in aggregation.

MongoDB

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

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

A$push

B$addToSet

C$sum

D$avg

Attempts:

3 left

💡 Hint

Common Mistakes

Using $sum or $avg instead of $push.

Confusing $push with $addToSet which avoids duplicates.

The $push accumulator adds values to an array during aggregation.

2fill in blank

medium

Complete the code to group documents by "type" and push "name" into an array.

MongoDB

db.products.aggregate([{ $group: { _id: "$type", names: { [1]: "$name" } } }])

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

A$push

B$max

C$sum

D$min

Attempts:

3 left

💡 Hint

Common Mistakes

Using $sum or $max which do not build arrays.

Forgetting to use $push inside $group.

$push collects all "name" values into an array for each "type" group.

3fill in blank

hard

Fix the error in the aggregation pipeline to correctly push "score" values into an array.

MongoDB

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

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

A$addToSet

B$avg

C$push

D$count

Attempts:

3 left

💡 Hint

Common Mistakes

Using $count which is not an accumulator for arrays.

Using $avg which calculates average instead of collecting values.

$push correctly accumulates all "score" values into an array per player.

4fill in blank

hard

Fill both blanks to group by "department" and push "employee" names into an array.

MongoDB

db.employees.aggregate([{ $group: { _id: [1], staff: { [2]: "$employee" } } }])

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

A"$department"

B$push

C$sum

D"department"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the field name without $ in _id.

Using $sum instead of $push for array building.

The _id must be the field to group by, here "$department", and $push collects employee names.

5fill in blank

hard

Fill all three blanks to group by "category", push "product" names, and filter only categories with more than 2 products.

MongoDB

db.products.aggregate([
  { $group: { _id: [1], products: { [2]: "$product" } } },
  { $match: { $expr: { $gt: [ { $[3]: "$products" }, 2 ] } } }
])

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

A"$category"

B$push

Clength

Dsize

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'length' instead of 'size' to check array length in $match.

Forgetting $ in the group _id field.

Group by "$category", use $push to collect products, and filter with size to check array length.