rails recursive method problem

Question

I'm having a problem trying to get a recursive method to work in rails/ruby. The purpose is to find all ancestor categories of a given category based on the parent_id. The current method does return the right ancestor categories, but it is nesting the array. I think this is because I'm initializing the category_ancestors array, and then it is getting reinitialized as the method recurses through itself. I'm trying to figure out how to change this so that I get a single level array with the category attributes rather than how it is outputting the data now.

def self.get_ancestors(category)

category_ancestors = []   # <-- this seems to be the problem

category_ancestors << category.attributes

if category.has_parent?
  category.get_parent.each do |parent_category|
    category_ancestors << get_ancestors(parent_category)
  end
end

category_ancestors.reverse

end

This returns something like which is nesting the arrays (but I need them all at the same level):

--- 
  - - - name: Category 1
    id: 1
    created_at: 2011-09-04 22:56:43.198413 Z
    updated_at: 2011-09-07 00:14:09.934813 Z
    parent:id 

 - name: Category 2
   id: 2
   created_at: 2011-09-04 22:56:43.198413 Z
   updated_at: 2011-09-07 00:14:09.934813 Z
   parent:id: 1

- name: Category 3
  id: 3
  created_at: 2011-09-04 22:56:43.198413 Z
  updated_at: 2011-09-07 00:14:09.934813 Z
  parent:id: 2

John Douthat · Accepted Answer · 2011-09-07 15:29:07Z

1

Here's a non-recursive version that does the same thing

class Category
  def ancestors
    result = []
    c = self
    while c.parent
      result.unshift(c.parent)
      c = c.parent
    end
    result
  end
end

answered Sep 7, 2011 at 15:29

John Douthat

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Comments

Winfield · Accepted Answer · 2011-09-07 15:29:39Z

0

If you need a flat array, you should use concat() to join the elements into a single array instead of ending up with an array of arrays.

  def self.get_ancestors(category)

    category_ancestors = []   # <-- this seems to be the problem

    category_ancestors << category.attributes

    if category.has_parent?
      category.get_parent.each do |parent_category|
        category_ancestors.concat(get_ancestors(parent_category))
      end
    end

    category_ancestors.reverse

  end

answered Sep 7, 2011 at 15:29

Winfield

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1 Comment

Frank Over a year ago

Thanks very much, I now see that I should have been using concat to keep things in a single array.

coder_tim · Accepted Answer · 2011-09-07 16:41:07Z

0

I would use something like this:

category_ancestors += get_ancestors(parent_category)

answered Sep 7, 2011 at 16:41

coder_tim

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