FAQ: Ordering Your Library - What You'll Be Building

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This community-built FAQ covers the “What You’ll Be Building” exercise from the lesson “Ordering Your Library”.

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This exercise can be found in the following Codecademy content:

Learn Ruby

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[rebeckabrax]

Hi, I’m just finishing up the “Ordering Your Library” lesson under Blocks and Sorting (section 5 in Ruby). It seems like this activity was to build a method to alphabetize, but the introduction paragraph on the first page (1 of 6) says that we’d be building a reverse alphabetize method!

Anyone else messed up by that introductory page?
Thanks for any insights.
Rebecka

[7226321346]

I have some problem understanding the code in the control flow:

if rev
     arr.sort { |item1, item2| item2 <=> item1 }
else
     arr.sort { |item1, item2| item1 <=> item2 }
end

Why do we get a reversed array from the else clause when item1 and item2 switch positions around the spaceship operator?

According to the instructions, the spaceship operator <=> returns 1, 0, or -1. Does the operator do anything else more than return a numeric value?

[jbradenclickfunnels]

Can I get some help understanding the extra steps this and the last chapter have us doing to sort and then reverse sort? I am brand new to Ruby, but I quickly realized that “array.sort!” and then “array.reverse!” sorts everything in ascending order and then in descending order. Why do these chapters have us doing the block code and all the extra steps? What am I missing?

[mtrtmk]

You are correct in that if our intent is simply to sort integers or strings in ascending/descending order, then the built-in available sort and reverse methods are perfectly suitable for the task and we don’t need these blocks of code.

However, the intent behind the exercises seems to be to equip us to handle more complex situations. If the sorting criteria is more convoluted, then we will need to write our own custom blocks of code. By understanding the simple and straightforward ascending/descending order blocks, we can familiarize ourselves us with the basic structure of the blocks and then we can implement our own logic/conditions for more complex sorting.

The basic structure of the blocks is that the sort method is going to go through an array. It will compare two elements at a time. We can either use the <=> operator or if-else conditions to handle different situations. Either of -1, 0 or 1 will be returned. If 1 is returned, then we will swap the two elements. If 0 or -1 is the returned, then we leave the elements in their current positions. The blocks in the exercise for ascending/descending sort familiarize us with this structure for the simple and straightforward situation. Once we understand the basic structure, we can write our own blocks with more complex conditions and rules.

For the simple sorting of strings, you are correct. array.sort! and array.reverse! without any blocks of code are suitable. For more about the sort method, here is a useful and detailed explanation by Tony DiNitto

ruby's <=> operator and sort method