Sort_by for custom sorting in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to sort the array of numbers in ascending order using sort_by.

Ruby

numbers = [5, 2, 9, 1]
sorted = numbers.sort_by { |n| [1] }
puts sorted

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

Anumbers

Bn

Csorted

Dn.to_s

Attempts:

3 left

💡 Hint

Common Mistakes

Using the whole array instead of the element inside the block.

Using a variable not defined in the block.

The block variable n represents each element. Using n as the key sorts by the number itself.

2fill in blank

medium

Complete the code to sort the array of words by their length using sort_by.

Ruby

words = ["apple", "pear", "banana", "fig"]
sorted = words.sort_by { |word| [1] }
puts sorted

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

Awords.length

Bword

Cword.length

Dword[0]

Attempts:

3 left

💡 Hint

Common Mistakes

Sorting by the whole word instead of its length.

Using the array's length instead of the word's length.

Sorting by word.length sorts words by their length.

3fill in blank

hard

Fix the error in the code to sort people by age using sort_by.

Ruby

people = [{name: "Anna", age: 30}, {name: "Bob", age: 25}]
sorted = people.sort_by { |person| [1] }
puts sorted.map { |p| p[:name] }

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

Aperson[:age]

Bperson.age

Cperson[age]

Dperson['age']

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation to access hash keys.

Using string keys instead of symbol keys.

Hashes use symbols as keys accessed with person[:age]. Using person.age causes an error.

4fill in blank

hard

Fill both blanks to sort an array of strings by their last character using sort_by.

Ruby

words = ["cat", "dog", "bird"]
sorted = words.sort_by { |word| word[1][2] }
puts sorted

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

A[-1]

B[0]

C.downcase

D.upcase

Attempts:

3 left

💡 Hint

Common Mistakes

Using [0] to get the first character instead of last.

Not normalizing case, causing unexpected order.

Using word[-1] gets the last character. Applying .downcase ensures case-insensitive sorting.

5fill in blank

hard

Fill all three blanks to sort an array of hashes by the length of the name in descending order using sort_by.

Ruby

people = [{name: "Anna"}, {name: "Elizabeth"}, {name: "Bob"}]
sorted = people.sort_by { |person| [1] [2] [3]1 }
puts sorted.map { |p| p[:name] }

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

Aperson[:name].length

B-

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Sorting ascending instead of descending.

Using dot notation for hash keys.

Missing the negative sign to reverse order.

To sort descending by name length, return negative lengths using - person[:name].length *1. Since sort_by sorts ascending on the returned values, more negative values (longer names) appear first.

Practice

1. What does the Ruby method sort_by do?

easy

A. Sorts elements based on a value you specify for each element.

B. Changes the original array to a sorted one.

C. Removes duplicate elements from an array.

D. Reverses the order of elements in an array.

Solution

1. Step 1: Understand the purpose of sort_by

   sort_by sorts elements by a value you choose for each element, like length or age.

2. Step 2: Compare with other array methods

   Unlike sort!, sort_by returns a new sorted array without changing the original.

3. Final Answer:

   Sorts elements based on a value you specify for each element. -> Option A

4. Quick Check:

   sort_by sorts by chosen value [OK]

Hint: Remember: sort_by sorts by a custom value, not in-place [OK]

Common Mistakes:

• Thinking sort_by changes the original array
• Confusing sort_by with reverse or uniq
• Assuming sort_by removes duplicates

2. Which of the following is the correct syntax to sort an array words by their length using sort_by?

easy

A. words.sort_by(word.length)

B. words.sort_by => word.length

C. words.sort_by { |word| word.length }

D. words.sort_by(word) { length }

Solution

1. Step 1: Recall Ruby block syntax for sort_by

   The correct syntax uses a block with curly braces and a block variable: array.sort_by { |item| expression }.

2. Step 2: Match syntax with the options

   words.sort_by { |word| word.length } correctly uses words.sort_by { |word| word.length }. Others have syntax errors or wrong usage.

3. Final Answer:

   words.sort_by { |word| word.length } -> Option C

4. Quick Check:

   sort_by needs a block with |variable| [OK]

Hint: Use curly braces and |var| for sort_by blocks [OK]

Common Mistakes:

• Passing arguments directly instead of using a block
• Using => instead of block braces
• Misplacing parentheses around block

3. What will be the output of this Ruby code?

people = [{name: "Anna", age: 30}, {name: "Bob", age: 25}, {name: "Cara", age: 35}]
sorted = people.sort_by { |person| person[:age] }
puts sorted.map { |p| p[:name] }

medium

A. ["Anna", "Bob", "Cara"]

B. ["Bob", "Anna", "Cara"]

C. ["Cara", "Anna", "Bob"]

D. ["Bob", "Cara", "Anna"]

Solution

1. Step 1: Understand sorting by age

   The array is sorted by the :age key in ascending order: 25, 30, 35.

2. Step 2: Map sorted array to names

   After sorting, the order is Bob (25), Anna (30), Cara (35). Mapping names gives ["Bob", "Anna", "Cara"].

3. Final Answer:

   ["Bob", "Anna", "Cara"] -> Option B

4. Quick Check:

   sort_by age ascending = [Bob, Anna, Cara] [OK]

Hint: Sort_by returns new array sorted by block value [OK]

Common Mistakes:

• Assuming sort_by sorts descending by default
• Confusing keys in hash access
• Not mapping to names after sorting

4. Identify the error in this code snippet:

items = ["apple", "pear", "banana"]
sorted = items.sort_by do |item|
  item.length
end
puts sorted

medium

A. No error; code works correctly

B. Incorrect block syntax for sort_by

C. Missing parentheses in sort_by call

D. Using sort_by instead of sort

Solution

1. Step 1: Check block syntax

   The block uses do |item| ... end, which is valid for sort_by.

2. Step 2: Verify sort_by usage

   sort_by accepts a block and returns a new array sorted by item length. No syntax or logic errors.

3. Final Answer:

   No error; code works correctly -> Option A

4. Quick Check:

   sort_by with do-end block is valid [OK]

Hint: do-end blocks work fine with sort_by [OK]

Common Mistakes:

• Thinking parentheses are mandatory around block
• Confusing sort_by with sort!
• Assuming sort_by modifies original array

5. Given an array of hashes representing products:

products = [
  {name: "Pen", price: 1.5, stock: 10},
  {name: "Notebook", price: 2.0, stock: 0},
  {name: "Eraser", price: 0.5, stock: 5}
]

How would you use sort_by to get products sorted by price but only include those with stock greater than zero?

hard

A. products.sort_by { |p| p[:stock] }.select { |p| p[:price] > 0 }

B. products.sort_by { |p| p[:price] if p[:stock] > 0 }

C. products.sort_by { |p| p[:stock] > 0 ? p[:price] : 0 }

D. products.select { |p| p[:stock] > 0 }.sort_by { |p| p[:price] }

Solution

1. Step 1: Filter products with stock > 0

   Use select to keep only products where stock is greater than zero.

2. Step 2: Sort filtered products by price

   Apply sort_by on the filtered array to sort by price.

3. Final Answer:

   products.select { |p| p[:stock] > 0 }.sort_by { |p| p[:price] } -> Option D

4. Quick Check:

   Filter then sort_by for correct result [OK]

Hint: Filter first, then sort_by for combined conditions [OK]

Common Mistakes:

• Trying to filter inside sort_by block
• Sorting by stock instead of price
• Selecting after sorting, which keeps unwanted items