Question

I am trying to write a function to convert a flat array with a path information into a tree representation of that array.

The goal would be to turn an array like the following:

[
{ :name => "a", :path => [ 'a' ] },
{ :name => "b", :path => [ 'a', 'b' ] },
{ :name => "c", :path => [ 'a', 'b', 'c' ] },
{ :name => "d", :path => [ 'a', 'd' ] },
{ :name => "e", :path => [ 'e' ] }
]

into one like this:

[{:node=>{:name=>"a", :path=>["a"]},
  :children=>
   [{:node=>{:name=>"b", :path=>["a", "b"]},
     :children=>
      [{:node=>{:name=>"c", :path=>["a", "b", "c"]}, :children=>[]}]},
    {:node=>{:name=>"d", :path=>["a", "d"]}, :children=>[]}]},
 {:node=>{:name=>"e", :path=>["e"]}, :children=>[]}]

The closest result I got with was with the following code:

class Tree

  def initialize
    @root = { :node => nil, :children => [ ] } 
  end 

  def from_array( array )
    array.inject(self) { |tree, node| tree.add(node) }
    @root[:children]
  end 

  def add(node)
    recursive_add(@root, node[:path].dup, node)
    self
  end 

  private

  def recursive_add(parent, path, node)
    if(path.empty?)
      parent[:node] = node
      return
    end 
    current_path = path.shift
    children_nodes = parent[:children].find { |child| child[:node][:path].last == current_path } 
    unless children_nodes
      children_nodes = { :node => nil, :children => [ ] } 
      parent[:children].push children_nodes
    end 
    recursive_add(children_nodes, path, node)
  end 
end

flat = [ 
  { :name => "a", :path => [ 'a' ] },
  { :name => "b", :path => [ 'a', 'b' ] },
  { :name => "c", :path => [ 'a', 'b', 'c' ] },
  { :name => "d", :path => [ 'a', 'd' ] },
  { :name => "e", :path => [ 'e' ] } 
]

require 'pp'
pp Tree.new.from_array( flat )

But it is quite verbose and I have the feeling that it might not be very effective for very large sets.

What would be the cleanest and most effective way to achieve that in ruby?

Answer 1

This is my try.

array = [
{ :name => "a", :path => [ 'a' ] },
{ :name => "b", :path => [ 'a', 'b' ] },
{ :name => "c", :path => [ 'a', 'b', 'c' ] },
{ :name => "d", :path => [ 'a', 'd' ] },
{ :name => "e", :path => [ 'e' ] }
]

array
.sort_by{|h| -h[:path].length}
.map{|h| {node: h, children: []}}
.tap{|array| 
  while array.first[:node][:path].length > 1
    child = array.shift
    array
    .find{|h| h[:node][:name] == child[:node][:path][-2]}[:children]
    .push(child)
  end
}

# => [
  {:node=>{:name=>"e", :path=>["e"]}, :children=>[]},
  {:node=>{:name=>"a", :path=>["a"]}, :children=>[
    {:node=>{:name=>"d", :path=>["a", "d"]}, :children=>[]},
    {:node=>{:name=>"b", :path=>["a", "b"]}, :children=>[
      {:node=>{:name=>"c", :path=>["a", "b", "c"]}, :children=>[]}
    ]}
  ]}
]