sort_by in ruby

Guri Bee

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21-10-2024

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Mastering sort_by in Ruby: A Comprehensive Guide

The sort_by method in Ruby is a powerful tool for arranging arrays in a specific order based on a custom criterion. While seemingly similar to sort, sort_by offers greater flexibility and efficiency when you need to prioritize elements based on a calculated value or attribute.

What does sort_by do?

Imagine you have an array of objects, like users with names and ages. You want to sort them by age, not alphabetically by name. That's where sort_by comes in. It takes a block as an argument, and this block defines how to extract the value used for comparison.

Example:

users = [
  { name: "Alice", age: 30 },
  { name: "Bob", age: 25 },
  { name: "Charlie", age: 35 }
]

sorted_users = users.sort_by { |user| user[:age] }
puts sorted_users
# Output: [{:name=>"Bob", :age=>25}, {:name=>"Alice", :age=>30}, {:name=>"Charlie", :age=>35}] 

In this case, sort_by takes each user object and uses the age attribute as the sorting criterion. This lets us sort the users in ascending order of their age.

Key Differences from sort

• Sorting Criterion: sort directly compares elements, while sort_by uses the result of applying the block to each element for comparison.
• Efficiency: sort_by is more efficient for sorting complex objects because it only needs to calculate the sorting criterion once per element, unlike sort which might need to compare multiple times.
• Mutability: sort_by returns a new sorted array, leaving the original array untouched, while sort modifies the original array in place.

Diving Deeper: Additional Features

Let's explore some practical scenarios where sort_by shines:

1. Sorting by Multiple Criteria:

Imagine you want to sort a list of movies first by genre, then by release date. You can achieve this by using a nested sort_by or by defining a custom sorting logic within the block.

movies = [
  { title: "The Matrix", genre: "Sci-Fi", release_year: 1999 },
  { title: "The Shawshank Redemption", genre: "Drama", release_year: 1994 },
  { title: "Inception", genre: "Sci-Fi", release_year: 2010 }
]

sorted_movies = movies.sort_by { |movie| [movie[:genre], movie[:release_year]] }
puts sorted_movies
# Output: [{:title=>"The Shawshank Redemption", :genre=>"Drama", :release_year=>1994}, {:title=>"The Matrix", :genre=>"Sci-Fi", :release_year=>1999}, {:title=>"Inception", :genre=>"Sci-Fi", :release_year=>2010}]

2. Sorting by Calculated Values:

You can utilize sort_by to sort based on calculated values. For example, sorting a list of users by their age difference with a specific target age.

users = [
  { name: "Alice", age: 30 },
  { name: "Bob", age: 25 },
  { name: "Charlie", age: 35 }
]

target_age = 32

sorted_users = users.sort_by { |user| (target_age - user[:age]).abs }
puts sorted_users
# Output: [{:name=>"Charlie", :age=>35}, {:name=>"Alice", :age=>30}, {:name=>"Bob", :age=>25}]

3. Sorting in Descending Order:

While sort_by defaults to ascending order, you can easily reverse the sorting by passing the reverse method to the result:

sorted_users_descending = users.sort_by { |user| user[:age] }.reverse
puts sorted_users_descending

Conclusion

sort_by offers a versatile and efficient way to sort your data in Ruby based on customized criteria. By understanding its mechanics and exploring its flexibility, you can leverage this powerful method to organize your arrays in meaningful ways.

Note: This article is inspired by discussions on the topic of sorting in Ruby on GitHub.

Further Exploration:

• For a deeper dive into sorting techniques and comparisons between sort and sort_by, explore the Ruby documentation.
• Check out various sorting examples on stackoverflow for practical implementations.