Ruby: Merge Hash containing Arrays

Question

I am trying to merge two Hashes.I got the code from here. As you can see I want to add one more hobby to my list. There are many hobbies. When h1 is formed ,only one hobby was available. When the second hobby arrived I wanted to merge it with the previous hash.

The structure of the Hashes are :

h1 = {"students"=>[{"name"=>"bobby", "hobbies"=>[{"outdoor"=>"cycling"}]}]}

h2 = {"students"=>[{"name"=>"bobby", "hobbies"=>[{"indoor"=>"reading"}]}]}

I ran this code:

res = h1.merge(h2) {|key,val1,val2| val1.merge val2}

The error I got was:

 undefined method `merge' for [{"name"=>"bobby", "hobbies"=>[{"outdoor"=>"cycling"}]}]:Array (NoMethodError)

So since array is involved, I don't know what to do. Any Help.

Required Output:

{"students"=>[{"name"=>"bobby", "hobbies"=>[{"outdoor"=>"cycling", "indoor"=>"reading"}]}]}

"pretty clear"? No, the hash would have been pretty clear if you wrote h1 = {"students"=>[{"name"=>"bobby", "hobbies"=>[{"outdoor"=>"cycling"}]}]}. Also, we don't know what you want to do. What do you want to happen when there are arrays present? Give the output example as well as input examples. — Amadan
– Amadan, Commented Mar 6, 2015 at 6:20
What’s the reason of storing hobbies as an array consisting of one hash element? — Aleksei Matiushkin
– Aleksei Matiushkin, Commented Mar 6, 2015 at 6:55
@mudasobwa. There are many hobbies. When h1 is formed ,only one hobby was available. When the second hobby arrived I wanted to merge it with the previous hash. — 0aslam0
– 0aslam0, Commented Mar 6, 2015 at 6:59
That explains why you do have hash there. It’s still unclear, why you decided to wrap hobbies hash in array. — Aleksei Matiushkin
– Aleksei Matiushkin, Commented Mar 6, 2015 at 7:01

Hasegawa Yoshinori · Accepted Answer · 2015-03-06 07:05:03Z

The built-in marge method cannot do what you want. You should write the original code to merge these structure like this.

def recursive_merge(h1, h2)
   case h1
   when Hash
      (h1.keys + h2.keys).each do |key|
         if h1.include?(key) && h2.include?(key) then
            recursive_merge(h1[key], h2[key])
         elsif h2.include?(key)
            h1[key] = h2[key]
         end
      end
   when Array
      for i in 0...([h1.count, h2.count].max)
         if i < h1.count && i < h2.count then
            recursive_merge(h1[i], h2[i])
         elsif i < h2.count then
            h1[i] = h2[i]
         end
      end
   end
end

recursive_merge(h1, h2)
puts h1

This method results the follwing output. Please note that this method overwrites h1 itself.

{"students"=>[{"name"=>"bobby", "hobbies"=>[{"outdoor"=>"cycling", "indoor"=>"reading"}]}]}

Aleksei Matiushkin · Accepted Answer · 2015-03-06 07:13:02Z

2

The answer on your question might be:

h1.merge(h2) { |k, v1, v2| 
  v1.map.with_index { |v1e, idx| 
    v1e['hobbies'].first.merge! v2[idx]['hobbies'].first
    v1e  
  }
  v1 
}

#⇒ {
#  "students" => [
#    [0] {
#      "hobbies" => [
#        [0] {
#           "indoor" => "reading",
#          "outdoor" => "cycling"
#        }
#      ],
#         "name" => "bobby"
#    }
#  ]
# }

But I would definitely redesign hobbies to be a hash, not an array of hashes, eliminating weird first calls:

v1e['hobbies'].merge! v2[idx]['hobbies']

Hope it helps.

edited Mar 6, 2015 at 7:13

answered Mar 6, 2015 at 7:01

Aleksei Matiushkin

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2 Comments

0aslam0 Over a year ago

Reality check , the actual Hash is very different and has technical names. For the sake of understanding, i tried to give it meaningful names. This works! But I can't understand what you wanted those variables to mean - |vle,idx|

Aleksei Matiushkin Over a year ago

v1, v2 stay for value1, value2. v1e stays for value1_element. idx is apparetnly an index.

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