Sort_by for custom sorting in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the sort_by method do in Ruby?

It sorts elements of a collection based on the value returned by the block you provide. It creates a new sorted array without changing the original.

beginner

How do you use sort_by to sort an array of strings by their length?

You pass a block that returns the length of each string: <br>array.sort_by { |str| str.length }

intermediate

Why might you choose sort_by over sort for custom sorting?

sort_by is often faster and simpler when sorting by a computed value because it calculates the sort keys once, then sorts by those keys.

beginner

What will this code output?<br>

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

It sorts words by their last letter:<br>["banana", "apple", "pear"] because 'a' < 'e' < 'r'.

intermediate

Can sort_by be used to sort by multiple criteria? How?

Yes. Return an array of values in the block, like:<br>array.sort_by { |x| [x.age, x.name] } to sort by age, then name.

What does sort_by return in Ruby?

A A new sorted array

B The original array sorted in place

C A boolean indicating if sorting succeeded

D The number of elements sorted

sort_by returns a new array sorted by the block's values, leaving the original unchanged.

Which block would sort an array of numbers by their absolute value?

A array.sort_by { |n| n.abs }

B array.sort_by { |n| -n }

C array.sort_by { |n| n }

D array.sort_by { |n| n.to_s }

Using n.abs sorts numbers by their absolute value.

What is a benefit of using sort_by instead of sort with a block?

A It modifies the original array

B It is slower but more readable

C It calculates sort keys once for efficiency

D It only works with numbers

sort_by calculates the sorting keys once, making it more efficient for complex sorting.

How would you sort an array of hashes by the value of the key :score?

A array.sort_by { |h| h.score }

B array.sort_by(:score)

C array.sort { |a, b| a[:score] <=> b[:score] }

D array.sort_by { |h| h[:score] }

You access the :score key inside the block to sort by it.

What will ["cat", "dog", "bird"].sort_by { |w| w.length } return?

A ["cat", "bird", "dog"]

B ["cat", "dog", "bird"]

C ["dog", "cat", "bird"]

D ["bird", "cat", "dog"]

It sorts words by length: cat (3), dog (3), bird (4). Since cat and dog have the same length, the stable sort preserves their original relative order.

Explain how sort_by works in Ruby and give an example of sorting strings by their last character.

Think about how you tell Ruby what to sort by using a block.

Describe how to sort an array of objects by multiple attributes using sort_by.

Use an array inside the block to specify multiple sort keys.