Array sorting and reversing in Ruby - Mini Project: Build & Apply

Array sorting and reversing

📖 Scenario: You work in a small bookstore. You have a list of book titles that customers want to buy. You want to organize this list to make it easier to find books.

🎯 Goal: You will create a list of book titles, then sort them alphabetically, and finally reverse the order to see the list from Z to A.

📋 What You'll Learn

Create an array called books with the exact titles: 'Ruby Basics', 'Learn Rails', 'JavaScript Guide', 'Python Essentials', 'Data Science'

Create a variable called sorted_books that holds the books array sorted alphabetically

Create a variable called reversed_books that holds the sorted_books array reversed

Print the reversed_books array

💡 Why This Matters

🌍 Real World

Sorting and reversing lists is common when organizing data like product names, customer lists, or any collection of items.

💼 Career

Many programming jobs require you to manipulate lists and arrays efficiently to prepare data for display or further processing.

1

Create the initial array of book titles

Create an array called books with these exact titles: 'Ruby Basics', 'Learn Rails', 'JavaScript Guide', 'Python Essentials', 'Data Science'

Ruby

# Create the array called books with the given titles
# Your code here

Hint

Use square brackets [] to create an array and separate each title with commas.

2

Sort the array alphabetically

Create a variable called sorted_books that holds the books array sorted alphabetically using the sort method

Ruby

books = ['Ruby Basics', 'Learn Rails', 'JavaScript Guide', 'Python Essentials', 'Data Science']
# Create sorted_books by sorting books alphabetically
# Your code here

Hint

Use sorted_books = books.sort to get a new sorted array.

3

Reverse the sorted array

Create a variable called reversed_books that holds the sorted_books array reversed using the reverse method

Ruby

books = ['Ruby Basics', 'Learn Rails', 'JavaScript Guide', 'Python Essentials', 'Data Science']
sorted_books = books.sort
# Create reversed_books by reversing sorted_books
# Your code here

Hint

Use reversed_books = sorted_books.reverse to reverse the sorted list.

4

Print the reversed array

Print the reversed_books array using puts

Ruby

books = ['Ruby Basics', 'Learn Rails', 'JavaScript Guide', 'Python Essentials', 'Data Science']
sorted_books = books.sort
reversed_books = sorted_books.reverse
# Print reversed_books
# Your code here

Hint

Use puts reversed_books to print each book title on its own line.

Practice

1. What does the Ruby method sort do when called on an array?

easy

A. It arranges the elements in ascending order.

B. It reverses the order of elements.

C. It removes duplicate elements.

D. It shuffles the elements randomly.

Solution

1. Step 1: Understand the purpose of sort

   The sort method arranges elements in ascending order by default.

2. Step 2: Compare with other methods

   Unlike reverse which flips order, sort orders elements from smallest to largest.

3. Final Answer:

   It arranges the elements in ascending order. -> Option A

4. Quick Check:

   sort = ascending order [OK]

Hint: Remember: sort arranges ascending, reverse flips order [OK]

Common Mistakes:

• Confusing sort with reverse
• Thinking sort removes duplicates
• Assuming sort shuffles elements

2. Which of the following is the correct syntax to reverse an array arr in Ruby?

easy

A. arr.reverse!

B. arr.reverse[]

C. reverse.arr()

D. arr.reverse()!

Solution

1. Step 1: Identify the correct method call

   The method to reverse an array in place is reverse! called on the array object.

2. Step 2: Check syntax correctness

   Only arr.reverse! is valid Ruby syntax; others are incorrect method calls or misplaced symbols.

3. Final Answer:

   arr.reverse! -> Option A

4. Quick Check:

   reverse! modifies array in place [OK]

Hint: Use reverse! to reverse array in place [OK]

Common Mistakes:

• Using parentheses incorrectly
• Placing exclamation mark after parentheses
• Calling reverse as a standalone function

3. What is the output of the following Ruby code?

arr = [3, 1, 4, 2]
sorted_arr = arr.sort
reversed_arr = sorted_arr.reverse
puts reversed_arr.inspect

medium

A. [1, 2, 3, 4]

B. [3, 1, 4, 2]

C. [4, 3, 2, 1]

D. [2, 4, 1, 3]

Solution

1. Step 1: Sort the original array

   Calling arr.sort returns a new array sorted ascending: [1, 2, 3, 4].

2. Step 2: Reverse the sorted array

   Calling sorted_arr.reverse flips the order to [4, 3, 2, 1].

3. Final Answer:

   [4, 3, 2, 1] -> Option C

4. Quick Check:

   sort then reverse = descending order [OK]

Hint: Sort then reverse = descending order [OK]

Common Mistakes:

• Assuming reverse modifies original array
• Confusing sorted array with original
• Expecting reverse to sort ascending

4. Identify the error in this Ruby code snippet:

arr = [5, 2, 9]
arr.sort!
arr.reverse
puts arr.inspect

medium

A. Missing parentheses in method calls cause errors.

B. The sort! method is invalid syntax.

C. The array arr cannot be reversed after sorting.

D. Using reverse does not change arr in place.

Solution

1. Step 1: Understand sort! effect

   sort! sorts the array arr in place, so arr becomes [2, 5, 9].

2. Step 2: Check reverse method usage

   reverse returns a new reversed array but does not modify arr itself.

3. Final Answer:

   Using reverse does not change arr in place. -> Option D

4. Quick Check:

   reverse without ! returns new array [OK]

Hint: Use reverse! to modify array in place [OK]

Common Mistakes:

• Assuming reverse changes original array
• Thinking sort! is invalid
• Believing method calls need parentheses always

5. Given an array arr = [7, 3, 5, 3, 9, 1], how can you create a new array that is sorted in descending order without changing the original array?

hard

A. Use arr.sort! then arr.reverse!

B. Use arr.sort.reverse

C. Use arr.reverse.sort

D. Use arr.reverse! then arr.sort!

Solution

1. Step 1: Sort the array without modifying original

   arr.sort returns a new sorted array ascending, original arr stays unchanged.

2. Step 2: Reverse the sorted array to get descending order

   Calling reverse on the sorted array returns a new array reversed, still not changing original.

3. Final Answer:

   Use arr.sort.reverse -> Option B

4. Quick Check:

   sort then reverse = descending new array [OK]

Hint: Chain sort then reverse to get descending without changing original [OK]

Common Mistakes:

• Using sort! or reverse! which modify original array
• Reversing before sorting
• Expecting reverse.sort to work the same