$first and $last accumulators in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the first document's name in each group.

MongoDB

{ $group: { _id: "$category", firstName: { [1]: "$name" } } }

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

A$first

B$sum

C$last

D$avg

Attempts:

3 left

💡 Hint

Common Mistakes

Using $last instead of $first will return the last document's value.

Using $sum or $avg will cause errors or unexpected results.

The $first accumulator returns the first value for the specified field in each group.

2fill in blank

medium

Complete the code to get the last document's score in each group.

MongoDB

{ $group: { _id: "$team", lastScore: { [1]: "$score" } } }

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

A$min

B$last

C$max

D$first

Attempts:

3 left

💡 Hint

Common Mistakes

Using $first will return the first document's value, not the last.

Using $max or $min will return the maximum or minimum values, not the last.

The $last accumulator returns the last value for the specified field in each group.

3fill in blank

hard

Fix the error in the aggregation pipeline to correctly get the first and last names.

MongoDB

[ { $group: { _id: "$department", firstEmp: { [1]: "$employee" }, lastEmp: { $last: "$employee" } } } ]

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

A$first

B$sum

C$max

D$avg

Attempts:

3 left

💡 Hint

Common Mistakes

Using $sum or $avg causes errors because they are not valid for string fields.

Using $max returns the maximum value, not the first.

The $first accumulator is needed to get the first employee's name; $last is already correct.

4fill in blank

hard

Fill both blanks to get the first and last order dates for each customer.

MongoDB

{ $group: { _id: "$customerId", firstOrder: { [1]: "$orderDate" }, lastOrder: { [2]: "$orderDate" } } }

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

A$first

B$last

C$max

D$min

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping $first and $last will give incorrect results.

Using $max or $min will return the highest or lowest dates, not the first or last.

Use $first for the first order date and $last for the last order date in each group.

5fill in blank

hard

Fill all three blanks to get the first product name, last product name, and maximum price in each category.

MongoDB

{ $group: { _id: "$category", firstProduct: { [1]: "$productName" }, lastProduct: { [2]: "$productName" }, maxPrice: { [3]: "$price" } } }

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

A$first

B$last

C$max

D$min

Attempts:

3 left

💡 Hint

Common Mistakes

Using $min instead of $max for price will give the lowest price, not the highest.

Mixing up $first and $last will swap the product names incorrectly.

Use $first for the first product, $last for the last product, and $max for the maximum price.