tsort

TSort

TSort implements topological sorting using Tarjan's algorithm for strongly connected components.

TSort is designed to be able to be used with any object which can be interpreted as a directed graph.

TSort requires two methods to interpret an object as a graph, tsort_each_node and tsort_each_child.

• tsort_each_node is used to iterate for all nodes over a graph.
• tsort_each_child is used to iterate for child nodes of a given node.

The equality of nodes are defined by eql? and hash since TSort uses Hash internally.

Installation

Add this line to your application's Gemfile:

gem 'tsort'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install tsort

Usage

The following example demonstrates how to mix the TSort module into an existing class (in this case, Hash). Here, we're treating each key in the hash as a node in the graph, and so we simply alias the required #tsort_each_node method to Hash's #each_key method. For each key in the hash, the associated value is an array of the node's child nodes. This choice in turn leads to our implementation of the required #tsort_each_child method, which fetches the array of child nodes and then iterates over that array using the user-supplied block.

require 'tsort'

class Hash
  include TSort
  alias tsort_each_node each_key
  def tsort_each_child(node, &block)
    fetch(node).each(&block)
  end
end

{1=>[2, 3], 2=>[3], 3=>[], 4=>[]}.tsort
#=> [3, 2, 1, 4]

{1=>[2], 2=>[3, 4], 3=>[2], 4=>[]}.strongly_connected_components
#=> [[4], [2, 3], [1]]

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test 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.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ruby/tsort.