Priora supplies an easy and intuitive way to prioritize a collection of objects in Ruby. It serves as a useful utility for working with a collection of several instances of some data class. Often, we would like to get that collection arranged according to some prioritization logic.
Instead of writing custom sorting blocks or implementing the spaceship operator (<=>) in your class, Priora offers a declarative style in order to obtain ready-for-consumption collections.

For example, let's assume we have a simple Post class, holding data regarding the author name, how many likes did it receive and whether this post is sponsored:

class Post
  attr_reader :author, :like_count, :is_sponsored

  def initialize(author:, like_count:, is_sponsored:)
    @author = author
    @like_count = like_count
    @is_sponsored = is_sponsored
  end
end

Then, in a given scenario, we have three instances at hand (these examples will be used throughout this README):

low_like_count_sponsored = Post.new(author: 'Jay C.', like_count: 10, is_sponsored: true)
high_like_count_unsponsored = Post.new(author: 'Aaron R.', like_count: 90, is_sponsored: false)
high_like_count_sponsored = Post.new(author: 'Don Y.', like_count: 90, is_sponsored: true)

Using Priora, we can easily get the collection prioritized according to our needs:

unprioritized_array = [high_like_count_unsponsored, low_like_count_sponsored, high_like_count_sponsored]
prioritized_array =  [high_like_count_sponsored, high_like_count_unsponsored, low_like_count_sponsored]
Priora.prioritize(unprioritized_array, by: [:like_count, :is_sponsored]) == prioritized_array
=> true

In case we can commit to the prioritization between Post objects - i.e. we do not need the flexibility of changing the priorities each time - we can include the Priora module in our class and declare the priorities using the prioritize_by class macro and gain shorter invocation. Our class would then read like this:

class Post
  include Priora
  prioritize_by :like_count, :is_sponsored

  attr_reader :author, :like_count, :is_sponsored

  def initialize(author:, like_count:, is_sponsored:)
    @author = author
    @like_count = like_count
    @is_sponsored = is_sponsored
  end
end

And getting the prioritized array would read like this:

Priora.prioritize(unprioritized_array) == prioritized_array
=> true

Using the prioritize_by class macro increases the readability of your code for the cost of flexibility. By adopting this usage, priorities are declared in-class and Priora can fetch it implicitly. For some cases this might be the right choice while for others the explicit style is more suitable.

One might come up with the following snippet as an equivalent solution:

unprioritized_array.sort { |a, b| [a.like_count, a.is_sponsored ? 1 : 0 ] <=> [b.like_count, b.is_sponsored ? 1 : 0] }.reverse == prioritized_array
=> true

Which is, of course, correct. However, I find several issues with this code:

• It is more verbose and prone to errors.
• It declares the prioritization logic twice.
• It handles the conversion of a boolean value (true / false) into a sortable value (1 / 0) inline, thus mixing levels of abstractions and confusing the potential reader.

Another possible alternative is implementing the spaceship operator (<=>) for Post instances, and then simply employ reverse sorting. I regard this approach as somewhat more elegant, but its main problem is that it assumes our sorting logic is always the same for a given class, which is not always true. Priora solves this problem by supporting the explicit by parameter.

I created Priora after having encountered a few scenarios in which I needed to get some collections prioritized in some specific manner, and having to supply these explicit blocks again and again was quite annoying. I figured out a modest library solving this problem could be nice to have.

Priora is based on the presumption that when we talk about a prioritized collection, we often refer to the outcome of sorting it and then reversing the result. This is because we naturally think about sorting in an ascending fashion, from small to large, while when we talk about "top priorities" we usually think of the largest items first.

Obviously, this is not always true and some prioritization processes should give precedence to smaller items first; Priora supports this scenario as well. You may change the prioritization direction for a specific priority:

Priora.prioritize(unprioritized_array, by: [[like_count: :asc], :is_sponsored])
=> [low_like_count_sponsored, high_like_count_sponsored, high_like_count_unsponsored]

We can see that the Post with the low like_count comes up first, however the two high like_count posts are prioritized by is_sponsored, so the sponsored Post comes up first.

If you have several priorities for which you wish to specify direction, you need to do so for each separately:

Priora.prioritize(unprioritized_array, by: [[like_count: :asc], [is_sponsored: :asc]])
=> [low_like_count_sponsored, high_like_count_unsponsored, high_like_count_sponsored]

As you might have noted, Priora also takes care of converting non-sortable values, such as true, false or nil, into sortable values. By default, it assumes that true is larger than false and that nil evaluates to 0.

You may override these implicit conversions with your own lambdas, as well as supply your own custom lambdas for other classes (and perhaps override their sorting logic!).

For example, if we wished to sort attributes of class String by their length, we could configure Priora accordingly beforehand:

Priora.configuration.add_conversion_lambda(String, lambda { |value| value.length })

Conversion lambdas are also removable, should that need arise:

Priora.configuration.remove_conversion_lambda(String)

Add this line to your application's Gemfile:

gem 'priora'

And then execute:

$ bundle

Or install it yourself as:

$ gem install priora

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/eliav-lavi/priora.

The gem is available as open source under the terms of the MIT License.