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The Ultimate Guide to Ruby Sorting

How many ways are there to sort an array in Ruby?

More than you think…

…even though Array only has two sorting methods (sort & sort_by) these methods can take a block, which allows you to sort in several different ways.

I want to share with you a few examples in this post.

You will also learn how to implement your own sorting method using the quick-sort algorithm.

Basic Sorting

The most basic form of sorting is provided by the Ruby sort method, which is defined in the Enumerable module.

Let’s see an example:

Notice that sort will return a new array with the results.

It’s also possible to sort “in-place” using the sort! method. This method modifies the current array instead of creating a new one.

Customized Sorting

Now let’s see more advanced sorting, like being able to sort by string length & things like that.

To do that we can use the sort_by method.

For example:

It is also possible to do this using the regular sort method with a block.

But in general & prefer the sort_by method because the intention is more clear, it’s easier to read & it is also a bit faster.

Note: This <=> symbol is called “the spaceship operator” & it’s a method you can implement in your class. It should return 1 (greater than), 0 (equal) or -1 (less than).

Reverse Sort

What about sorting in reverse?

You could use the reverse method after sorting, or you can use a block & put a minus sign in front of the thing you are sorting.

Let me show you an example:

Alphanumeric Sorting

Let’s say you want to sort a list of strings that contain numbers.

Like this:

By default you will not get this list sorted like you want:

But you can fix this using sort_by:

I used a regular expression (\d+) to match the numbers, then get the first number (first) & convert it to an integer object (to_i).

Sorting Hashes

You are not limited to sorting arrays, you can also sort a hash.

Example:

This will sort by value, but notice something interesting here, what you get back is not a hash.

You get a multi-dimensional array when sorting a hash.

To turn this back into a hash you can use the Array#to_h method.

QuickSort Implementation

Just for fun let’s implement our own sorting method. This is going to be slower than the built-in sort methods, but it’s still an interesting exercise if you like computer science.

The idea of quick sort is to pick one number at random then divide the list we are sorting into two groups.

One group is the numbers less than the chosen number & the other group is the numbers bigger than the chosen number.

Then we just repeat this operation until the list is sorted.

Benchmarks

Let’s see how all these sorting methods compare to each other in terms of performance.

Ruby 2.4.0:

As you can see the regular sort method is a lot faster than sort_by, but it’s not as flexible unless you use a block.

Video

Summary

You have learned how to use the sort & the sort_by methods to sort your arrays & hashes in different ways. You have also learned about the performance differences & how to implement the quicksort algorithm.

Don’t forget to share this post so more people can learn 🙂

Leave a Comment:

14 comments
Anand says 3 weeks ago

The Alphanumeric sorting input array (music) does not match the sorted array data.

Reply
    Jesus Castello says 3 weeks ago

    Sorry! I fixed it now 🙂

    Reply
Demba says 3 weeks ago

Thanks for these great articles. Your site is also very neat.

Reply
    Jesus Castello says 3 weeks ago

    Thanks for reading 🙂

    Reply
David Jenkins says 3 weeks ago

Hi, thanks for publishing this great guide. Just wanted to alert you to a typo:

In the Alphanumeric Sorting section, your array starts like this:

music = %w(21.mp3 50.mp3 1.mp3 40.mp3)

but then the results if music.sort are displayed as this:

[“10.mp3”, “21.mp3”, “40.mp3”, “5.mp3”]

i.e., 1.mp3 changed to 10.mp3 and 50.mp3 changed to 5.mp3

Feel free to delete this comment if you want.

Reply
    Jesus Castello says 3 weeks ago

    Thank you David!

    I fixed that 🙂

    Reply
Klaus says 3 weeks ago

Your quicksort implementation will not deal properly with arrays containing duplicates, as the pivot element (number) is only included once.

Reply
    Jesus Castello says 3 weeks ago

    You are right! I updated the code to make it work with duplicates 🙂

    Reply
Mr. Ahmed says 3 weeks ago

Great! Thanks 🙂

Reply
    Jesus Castello says 3 weeks ago

    Thanks for reading!

    Reply
Ankur says 3 weeks ago

Great and helpful article! Keep up the good work !! 🙂

Reply
    Jesus Castello says 3 weeks ago

    Thank you 🙂

    Reply
Vedran says a couple of weeks ago

No need for “s.scan(/\d+/).first.to_i” if the number is at the begining of string, just simple “s.to_i” would do the job.

Reply
    Jesus Castello says a couple of weeks ago

    Thanks for your comment 🙂

    Reply
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