Array expressions ($size, $arrayElemAt, $filter) in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the size of the array field 'scores'.

MongoDB

{ $size: "$ [1] " }

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

Avalues

Bscore

Cscores

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong field name like 'score' instead of 'scores'.

Forgetting to use quotes around the field name.

The $size operator returns the number of elements in the array. Here, the array field is named scores.

2fill in blank

medium

Complete the code to get the first element of the 'grades' array using $arrayElemAt.

MongoDB

{ $arrayElemAt: [ "$grades", [1] ] }

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

A1

B0

C-1

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as the index which returns the second element.

Using negative indexes which are not supported here.

The $arrayElemAt operator uses zero-based indexing. To get the first element, use index 0.

3fill in blank

hard

Fix the error in the $filter expression to select elements greater than 10 from 'values'.

MongoDB

{ $filter: { input: "$values", as: "item", cond: { $gt: [ "$$ [1] ", 10 ] } } }

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

Avalue

Belement

Cval

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different variable name than declared in 'as'.

Forgetting the double dollar signs ($$) before the variable.

The variable name used in as is item. To refer to it inside cond, use $$item.

4fill in blank

hard

Fill both blanks to filter 'scores' array for values less than 50 and get its size.

MongoDB

{ $size: { $filter: { input: "$scores", as: "score", cond: { $lt: [ "$$ [1] ", [2] ] } } } }

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

Ascore

Bvalue

C50

D100

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong variable name in the condition.

Using a wrong number for comparison.

The variable name is score as declared in as. The condition checks if score is less than 50.

5fill in blank

hard

Fill all three blanks to get the second element of filtered 'items' array where elements are greater than 5.

MongoDB

{ $arrayElemAt: [ { $filter: { input: "$items", as: "elem", cond: { $gt: [ "$$ [1] ", [2] ] } } }, [3] ] }

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

Aelem

B5

C1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable name in condition.

Using wrong comparison number.

Using wrong index for the second element.

The variable name is elem. The condition filters elements greater than 5. The second element has index 1.