convert from a 2d array to nested_set in Ruby on rails

Question

I have a tree structure in a .csv file (nodes are of type text), and after reading the csv i want to store the data in a ruby object. I went through a few tree plugins and i think nested_set would serve the purpose for me. However, i am facing problem with fixing a format of csv file, so that i can read it and convert into tree object. Is there any direct way of converting a csv file or 2 dimensional array, into a tree data structure??

Answer 1

After you clarified that you don't need to store this tree in database, I suggest to throw away NestedSets (they're to store nested sets of objects on RDBMS, which you don't need). What you need i simple tree

class Node
  attr_accessor :parent, :children, :text

  def initialize(text)
    @text = text
    @children = []
  end
end

As I have right to choose format of CSV file, then I suggest sth like this:

id,parent,text
1,,"1"
2,1,"1.1"
3,1,"1.2"
3,2,"1.1.1"

Tree root is first row, without parent, and there is always order that parent is declared before its children. That way you can build tree

def build_tree(rows)
  nodes = {}
  rows.each do |row|
    node = Node.new(row[:text])
    nodes[row[:id]] = node

    node.parent = nodes[row[:parent]]
    nodes[row[:parent]].children << node if row[:parent]
  end

  nodes.values.find {|node| node.parent.nil? }
end

root = build_tree(rows)
root.text #=> "1"
root.children.map(&:text) #=> ["1.1", "1.2"]
root.children[0].children.map(&:text) #=> ["1.1.1"]

If you need to get all texts from subnodes, then you need to use more tricks

def get_nodes(tree_node)
  [ tree_node, tree_node.children.map{|node| get_nodes(node)} ].flatten
end

get_nodes(root).map(&:text) #=> ["1", "1.1", "1.1.1", "1.2"]