Search for key-value from array of nested hash in ruby

Question

I have array of nested hash that is,

@a = [{"id"=>"5", "head_id"=>nil,
         "children"=>
             [{"id"=>"19", "head_id"=>"5",
                 "children"=>
                     [{"id"=>"21", "head_id"=>"19", "children"=>[]}]},
             {"id"=>"20", "head_id"=>"5",
                 "children"=>
                     [{"id"=>"22", "head_id"=>"20", "children"=>[]}, {"id"=>"23"}]
             }]
     }]

I need array of all values which have key name 'id'. like @b = [5,19,21,20,22,23] I have already try this '@a.find { |h| h['id']}`. Is anyone know how to get this?

Thanks.

This also works: @a.to_s.scan(/(?<=\"id\"=>\")\d+/).map(&:to_i) #=> [5, 19, 21, 20, 22, 23]. — Cary Swoveland
– Cary Swoveland, Commented Dec 23, 2014 at 18:37

Nermin · Accepted Answer · 2014-12-23 11:04:27Z

5

You can create new method for Array class objects.

class Array
  def find_recursive_with arg, options = {}
    map do |e|
      first = e[arg]
      unless e[options[:nested]].blank?
        others = e[options[:nested]].find_recursive_with(arg, :nested => options[:nested])
      end
      [first] + (others || [])
    end.flatten.compact
  end
end

Using this method will be like

@a.find_recursive_with "id", :nested => "children"

answered Dec 23, 2014 at 11:04

Nermin

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3 Comments

Nithin Over a year ago

I can't seem to find how does map work here. If you can give an explanation it would be nice.

Rajdeep Singh Over a year ago

plus one for the solution

Nermin Over a year ago

map is similar to each difference is that each returns array on which you have called it, but map replace e element with last line in this example [first] + (others || []) will be replaced with every element in array. see also Ruby map

Rajdeep Singh · Accepted Answer · 2014-12-23 12:18:20Z

4

It can be done like this, using recursion

def traverse_hash
  values = []
  @a = [{"id"=>"5", "head_id"=>nil,
     "children"=>
         [{"id"=>"19", "head_id"=>"5",
             "children"=>
                 [{"id"=>"21", "head_id"=>"19", "children"=>[]}]},
         {"id"=>"20", "head_id"=>"5",
             "children"=>
                 [{"id"=>"22", "head_id"=>"20", "children"=>[]}, {"id"=>"23"}]
         }]
 }] 
 get_values(@a)
end

def get_values(array)   
  array.each do |hash|        
    hash.each do |key, value|
      (value.is_a?(Array) ? get_values(value) : (values << value)) if key.eql? 'id'
    end
  end    
end

edited Dec 23, 2014 at 12:18

answered Dec 23, 2014 at 11:09

Rajdeep Singh

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