Sort an array of string in descending order

Question

Say I want to sort an array of strings in Ruby in descending order. So for example:

books = ["Charlie and the Chocolate Factory", "War and Peace", "Utopia", "A Brief History of Time", "A Wrinkle in Time"]

I'm currently going through Code Academy's Ruby course and they say to use the following code to achieve this:

books.sort! { |firstBook, secondBook| secondBook <=> firstBook }

However, couldn't this also be done by simply writing the following?

books.sort!.reverse

They both produce the same result on the Code Academy lesson but I was wondering if there what the difference was between the two.

Possible duplicate of Sorting an array in descending order in Ruby — Jon Schneider
– Jon Schneider, Commented Mar 14, 2019 at 18:19

Billy Chan · Accepted Answer · 2014-06-23 02:45:47Z

4

There is a slight performance difference between the two

This one is just one step of sort

books.sort! { |firstBook, secondBook| secondBook <=> firstBook }

This one actually contains two steps: sort and reverse

books.sort!.reverse

So, when the data is large the first one is preferred. However, in normal cases the second one would be simpler to write and the slight difference on performance doesn't matter that much.

answered Jun 23, 2014 at 2:45

Billy Chan

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Comments

Anurag Soni · Accepted Answer · 2014-06-23 02:03:11Z

1

I think that the tutorial was just trying to help you understand the <=> (spaceship operator) and how sorting is affected by the order of the variables. books.sort!.reverse is something that you would use more commonly.

answered Jun 23, 2014 at 2:03

Anurag Soni

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3 Comments

codedude Over a year ago

Ok. I guess that makes sense. I thought perhaps this was bad form or not allowed. Thanks!

Anurag Soni Over a year ago

You might like codeschool's tryruby.org or 'learn ruby the hard way' if you liked the ruby course on codeacademy. I found those to be a better starter's course for ruby with more explanations about the way things work.

codedude Over a year ago

I'm actually going through a couple web sites right now. I'll take a look at your suggestions

Imanol Alvarez · Accepted Answer · 2017-05-18 15:24:45Z

0

try with these options:

1. books.sort!{ |firstBook, secondBook| secondBook <=> firstBook }

2. books.sort{ |firstBook, secondBook| firstBook <=> secondBook  }

3. books.sort_by{ |Book| Book}.reverse

answered May 18, 2017 at 15:24

Imanol Alvarez

1

2 Comments

Nuageux Over a year ago

You should not digging an old post (with accepted answer), without answering the question (which was about the difference between the two command).

Imanol Alvarez Over a year ago

Sorry you're right, I just wanted to help. Regards!

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