Sort_by for custom sorting in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of custom sort_by with string length

What is the output of this Ruby code?

Ruby

words = ["apple", "pear", "banana", "fig"]
sorted = words.sort_by { |word| word.length }
puts sorted.join(",")

A pear,fig,apple,banana

B fig,pear,apple,banana

C fig,apple,pear,banana

D banana,apple,pear,fig

💡 Hint

Think about sorting words by their length from shortest to longest.

The sort_by block returns the length of each word. The words are sorted from shortest to longest length: "fig" (3), "pear" (4), "apple" (5), "banana" (6).

❓ Predict Output

intermediate

Sorting hashes by a nested value using sort_by

What will this Ruby code print?

Ruby

items = [{name: "a", price: 10}, {name: "b", price: 5}, {name: "c", price: 20}]
sorted = items.sort_by { |item| item[:price] }
puts sorted.map { |i| i[:name] }.join("")

A bac

B abc

C cab

D bca

💡 Hint

Look at the price values and sort from lowest to highest.

The sort_by sorts hashes by their :price key ascending: 5 (b), 10 (a), 20 (c). So the names in order are "b", "a", "c".

🔧 Debug

advanced

Identify the error in this sort_by usage

This Ruby code is intended to sort numbers by their remainder when divided by 3. What error does it raise?

Ruby

numbers = [4, 9, 7, 2]
sorted = numbers.sort_by { |n| n % }
puts sorted.join(",")

A TypeError: no implicit conversion of Symbol into Integer

B No error, outputs: 9,4,7,2

C ArgumentError: wrong number of arguments (given 0, expected 1)

D SyntaxError: unexpected end-of-input, expecting expression

💡 Hint

Check the block syntax and the use of the modulo operator.

The code uses 'n %' which is incomplete syntax for modulo operation. Ruby expects an operand after '%'. This causes a SyntaxError.

❓ Predict Output

advanced

Custom sorting with multiple criteria using sort_by

What is the output of this Ruby code?

Ruby

data = [["apple", 2], ["banana", 1], ["pear", 2], ["fig", 1]]
sorted = data.sort_by { |fruit, count| [count, fruit] }
puts sorted.map(&:first).join(",")

A banana,fig,apple,pear

B fig,banana,apple,pear

C banana,fig,pear,apple

D apple,pear,banana,fig

💡 Hint

Sort first by count ascending, then by fruit name ascending.

The sort_by sorts by count first: 1 then 2. For count=1, fruits are "banana", "fig" sorted alphabetically. For count=2, fruits are "apple", "pear" sorted alphabetically. So order is banana, fig, apple, pear.

🧠 Conceptual

expert

Understanding sort_by stability in Ruby

Given this Ruby code, what will be the output and why?

Ruby

arr = ["b", "a", "c", "a"]
sorted = arr.sort_by { |x| x }
puts sorted.join("")

A abc a (sort_by sorts but reverses equal elements order)

B aa bc (sort_by is unstable, order of equal elements may change)

C aabc (sort_by is stable, original order of equal elements preserved)

D cbaa (sort_by sorts descending)

💡 Hint

Think about whether sort_by keeps the order of elements that compare equal.

Ruby's sort_by is stable, meaning elements that compare equal keep their original order. The two "a" elements remain in the same order as in the original array.