Array comparison and set operations in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if two arrays are equal.

Ruby

arr1 = [1, 2, 3]
arr2 = [1, 2, 3]
puts arr1 [1] arr2

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

A==

B!=

C===

Dequal?

Attempts:

3 left

💡 Hint

Common Mistakes

Using equal? which checks object identity, not content equality.

Using != which checks inequality.

In Ruby, == checks if two arrays have the same elements in the same order.

2fill in blank

medium

Complete the code to find the intersection of two arrays.

Ruby

arr1 = [1, 2, 3, 4]
arr2 = [3, 4, 5, 6]
common = arr1 [1] arr2
puts common.inspect

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

A&

B-

C|

D^

Attempts:

3 left

💡 Hint

Common Mistakes

Using | which returns union, not intersection.

Using - which returns difference.

The & operator returns elements common to both arrays (intersection).

3fill in blank

hard

Fix the error in the code to get the union of two arrays.

Ruby

arr1 = [1, 2]
arr2 = [2, 3]
union = arr1 [1] arr2
puts union.inspect

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

A+

B|

C&

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using + which concatenates but does not remove duplicates.

Using & which returns intersection.

The | operator returns the union of two arrays without duplicates.

4fill in blank

hard

Fill both blanks to create a hash with array elements as keys and their lengths as values, only for words longer than 3 letters.

Ruby

words = ["cat", "lion", "tiger", "dog"]
lengths = {word[1] for word in words if word[2] 3}
puts lengths.inspect

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

A => word.length

B >

C <

D ==

Attempts:

3 left

💡 Hint

Common Mistakes

Using < or == which filter wrong words.

Forgetting the hash rocket => in the hash comprehension.

The code creates a hash where keys are words and values are their lengths, filtering words longer than 3 letters.

5fill in blank

hard

Fill all three blanks to create a hash with uppercase words as keys, their lengths as values, only for words longer than 3 letters.

Ruby

words = ["apple", "bat", "carrot", "dog"]
result = {word[1]: [2] for word in words if word.length [3] 3}
puts result.inspect

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

A.upcase()

Blen(word)

C>

Dword.length

Attempts:

3 left

💡 Hint

Common Mistakes

Using len(word) which is Python syntax, not Ruby.

Using wrong comparison operators.

The code creates a hash with uppercase words as keys and their lengths as values, filtering words longer than 3 letters.

Practice

1.

Which operator in Ruby returns the common elements between two arrays?

[1, 2, 3] ? [2, 3, 4]

easy

A. & (intersection)

B. | (union)

C. - (difference)

D. == (equality)

Solution

1. Step 1: Understand the operators

   The & operator returns elements common to both arrays.

2. Step 2: Apply to example arrays

   For arrays [1, 2, 3] and [2, 3, 4], common elements are 2 and 3.

3. Final Answer:

   & (intersection) -> Option A

4. Quick Check:

   Common elements = & [OK]

Hint: Use & for common items between arrays [OK]

Common Mistakes:

• Confusing union (|) with intersection (&)
• Using - for common elements
• Thinking == compares elements regardless of order

2.

Which of the following is the correct syntax to find the difference between two arrays a and b in Ruby?

easy

A. a == b

B. a - b

C. a | b

D. a & b

Solution

1. Step 1: Recall difference operator

   The - operator returns elements in a not in b.

2. Step 2: Confirm syntax correctness

   Using a - b is the correct Ruby syntax for difference.

3. Final Answer:

   a - b -> Option B

4. Quick Check:

   Difference = - [OK]

Hint: Use a - b to get items in a but not in b [OK]

Common Mistakes:

• Using & instead of - for difference
• Using | which is union
• Using == which checks equality

3.

What is the output of the following Ruby code?

a = [1, 2, 3, 4]
b = [3, 4, 5, 6]
result = a | b
puts result.inspect

medium

A. [1, 2, 3, 4, 5, 6]

B. [3, 4]

C. [1, 2]

D. [1, 2, 3, 4]

Solution

1. Step 1: Understand the union operator

   The | operator combines all unique elements from both arrays.

2. Step 2: Apply union to arrays

   Arrays a and b combined uniquely are [1, 2, 3, 4, 5, 6].

3. Final Answer:

   [1, 2, 3, 4, 5, 6] -> Option A

4. Quick Check:

   Union = | [OK]

Hint: Use | to combine unique elements from both arrays [OK]

Common Mistakes:

• Confusing union with intersection
• Expecting duplicates in output
• Using - which removes elements

4.

Identify the error in the following Ruby code snippet:

a = [1, 2, 3]
b = [2, 3, 4]
result = a & b
puts result

What is the problem?

medium

A. Syntax error due to missing parentheses

B. Outputs all elements from both arrays

C. Runtime error because & is not defined for arrays

D. No error; code runs and outputs common elements

Solution

1. Step 1: Check syntax and operators

   The & operator is valid for arrays to find intersection.

2. Step 2: Verify output behavior

   The code outputs common elements [2, 3] without error.

3. Final Answer:

   No error; code runs and outputs common elements -> Option D

4. Quick Check:

   Intersection & works fine [OK]

Hint: & works for arrays to find common items without syntax errors [OK]

Common Mistakes:

• Thinking & causes syntax error
• Expecting union instead of intersection
• Confusing output with difference

5.

You have two arrays representing user IDs:

active_users = [101, 102, 103, 104, 105]
inactive_users = [103, 105, 107]

Which Ruby expression gives you the list of users who are active but not inactive?

hard

A. active_users | inactive_users

B. active_users & inactive_users

C. active_users - inactive_users

D. active_users == inactive_users

Solution

1. Step 1: Understand the problem

   We want users in active_users but not in inactive_users.

2. Step 2: Use difference operator

   The - operator returns elements in first array not in second.

3. Step 3: Apply to given arrays

   active_users - inactive_users = [101, 102, 104]

4. Final Answer:

   active_users - inactive_users -> Option C

5. Quick Check:

   Difference = - [OK]

Hint: Use - to exclude inactive from active users [OK]

Common Mistakes:

• Using & which gives only common users
• Using | which combines all users
• Using == which checks equality