How to deep merge two nested Hashes of Arrays in Ruby?

Question

I'm trying to merge two nested array of array of hashes.

h1 = {:f => [{:f => [{:name => "a","type"=>"t",:mode=>"n"},{:name => "b","type"=>"t",:mode=>"n"}], :name => "p",:t=>"r"}]}

h2 = {:f => [{:f => [{:name => "a","type"=>"t",:mode=>"n"},{:name => "c","type"=>"t",:mode=>"n"}], :name => "p",:t=>"r"}]}

Here's what I'm expecting as output.

{:f => [{:f => [{:name => "a","type"=>"t",:mode=>"n"},{:name => "b","type"=>"t",:mode=>"n"},{:name => "c","type"=>"t",:mode=>"n"}], :name => "p",:t=>"r"}]}

I've used deep_merge & deep_merge! However that doesn't give me desired outcome. Appreciate any pointers.

Thanks, Navneet

Answer 1

As noted in comment there will be no general solution for what you want. The code below should work for your nesting structure (and is extremely ugly):

{f: [h1[:f].first.deep_merge(h2[:f].first) { |key, old, new| old == new ? new : (Array.wrap(old) + Array.wrap(new)).uniq }]}

The question is - why do you need to do this? Most likely there is better way to do what you are trying to achieve by this.

Answer 2

Here's what I wrote to solve it:

    class ::Array
     def mergeFields(second)
      second.each do |sElem|
       match = false
       self.each do |fElem|
        puts "Comparing: #{sElem[:name]} and #{fElem[:name]}"
        if sElem[:name] == fElem[:name]
         if !sElem[:fields].nil? && !fElem[:fields].nil? && sElem[:fields].is_a?(Array) && fElem[:fields].is_a?(Array)
          fElem[:fields].mergeFields(sElem[:fields])
         end  
         match = true
         break
        end
       end
       if match == false
        self << sElem  
       end 
      end
     end
    end

    h1 = {:fields => [{:fields => [{:name => "a","type"=>"t",:mode=>"n"},{:name => "b","type"=>"t",:mode=>"n"}], :name => "p",:t=>"r"},{:name => "e", :t => "s", :m => "n"}]}


    h2 = {:fields => [{:fields => [{:name => "a","type"=>"t",:mode=>"n"},{:name => "c","type"=>"t",:mode=>"n"}], :name => "p",:t=>"r"},{:name => "q", :t => "s", :m => "n"}]}

    h1[:fields].mergeFields(h2[:fields])