Pomona

Pomona is a simple, lightweight gem for creating and managing tree data structures in Ruby. It works using a custom data structure (the Tree) to contain small hashes of data (the Nodes) that can be queried and searched.

And of course it's a subtle, shameless Harry Potter reference.

Add this line to your application's Gemfile:

gem 'pomona'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install pomona

###Basics

Using Pomona is simple - to create a new Tree simply run:

tree = Tree.new

# Tree is now created as so:
{
   tree_array: []
}

Once you have your tree you can simply add any nodes to it by using #add_node like so:

tree.add_node({ data: "Your Data"})

After creation your new Node will automatically have a unique auto-generated id and an empty children array added to it. It will now look like this:

{
    tree_array: [
    	{ id: 1, data: "Your Data", children: [] }
    ]
}

You can now attach any additional (child) Nodes onto the one you've created by simply specifying the id when adding the Node.

tree.add_node({ data: "New Data" }, 1)

This will attach the Node to your previously created one, making the tree look like this:

{
    tree_array: [
    	{ id: 1, data: "Your Data", children: [
    		{ id: 2, data: "New Data", children: [] }
    	]}
    ]
}

###Searching the Tree Given the following example tree:

{
  tree_array: [
    { name: "Rickon Stark", id: 1, children: [
        { name: "Brandon Stark", id: 2, children: [] },
        { name: "Eddard Stark", id: 3, children: [
            { name: "Robb Stark", id: 6, children: [] },
            { name: "Sansa Stark", id: 7, children: [] },
            { name: "Arya Stark", id: 8, children: [] },
            { name: "Bran Stark", id: 9, children: [] },
            { name: "Rickon Stark II", id: 10, children: [] },
          ]
         },
         { name: "Lyanna Stark", id: 4, children: [
                { name: "Jon Snow", id: 11, children: [] },
            ]
         },
         { name: "Benjen Stark", id: 5, children: [] }
      ]
    }
  ]
}

We can search and aggregate any data from this by using the following commands:

Find will return the Node with the id you've passed as a paramater:

tree.find(8)
 { name: "Arya Stark", id: 8, children: [] }

Values_at works very similarly to its Hash counterpart with two primary differences:

1. It is able to take in an array of keys that it will search with, or a singular key you want to find.
2. It will return a nested Array if an array of keys is passed, or a flattened array if only one is passed.

# Multiple Keys

tree.values_at([:id, :name])
[
   ["Rickon Stark", 1], ["Brandon Stark", 2], ["Eddard Stark", 3],
   ["Robb Stark", 6], ["Sansa Stark", 7], ["Arya Stark", 8],
   ["Bran Stark", 9], ["Rickon Stark II", 10], ["Lyanna Stark", 4],
   ["Jon Stark", 11], ["Benjen Stark", 5]
]

# One Key
tree.values_at(:id)
[
	1, 2, 3, 6, 7, 8, 9, 10, 4, 11, 5
]

###Deleteing from the Tree To remove a Node from the tree simply use the remove_node method on your Tree object, specifying the id of the Node you wish to remove.

NOTE: This method will delete any children of the Node you've deleted as well, as they are now orphaned data.

tree.remove_node(3)

{
  tree_array: [
    { name: "Rickon Stark", id: 1, children: [
         { name: "Brandon Stark", id: 2, children: [] },
	     { name: "Lyanna Stark", id: 4, children: [
	         { name: "Jon Snow", id: 11, children: [] },
	       ]
	     },
	     { name: "Benjen Stark", id: 5, children: [] }
      ]
    }
  ]
}

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/pomona. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

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