Flatten Hash while Iterating over hash's array elements. Ruby

Question

The input hash can have nests of any combo of Arrays and Hashes (AoA, AoH, HoH, and HoA). Flatting the hash elements to have the proper key and delimiter of _> is no problem.

However, I'm having trouble when an Array comes into the picture and I need to grab each element and stick it to the proper key while continuing to build the output. The final output should be a 1-D array of hashes with the only difference being the each array elements.

For example:

if the input hash is: {:x => 333, :y => 13, :z => [1,2,{:zz => [40,50]},[10,20]], :a => {:o => "1", :p => "2"}}

The final result should be:

`[{:x => 333, :y => 13, :z => 1, :z_>zz => 40, :a_>o => 1, a_>p => 2},  
 {:x => 333, :y => 13, :z => 1, :z_>zz => 50, :a_>o => 1, a_>p => 2},  
 {:x => 333, :y => 13, :z => 2, :z_>zz => 40, :a_>o => 1, a_>p => 2},  
 {:x => 333, :y => 13, :z => 2, :z_>zz => 50, :a_>o => 1, a_>p => 2},  
 {:x => 333, :y => 13, :z => 10, :z_>zz => 40, :a_>o => 1, a_>p => 2},  
 {:x => 333, :y => 13, :z => 10, :z_>zz => 50, :a_>o => 1, a_>p => 2},  
 {:x => 333, :y => 13, :z => 20, :z_>zz => 40, :a_>o => 1, a_>p => 2},  
 {:x => 333, :y => 13, :z => 20, :z_>zz => 50, :a_>o => 1, a_>p => 2}]`

I have flatten the input hash using a recursive hash flatten. If the value is an array it loops through pushing {theKey => theKeysValue} onto an array for access later. — rsmets
– rsmets, Commented Aug 7, 2013 at 19:22

hirolau · Accepted Answer · 2013-10-22 14:32:45Z

This is long and complicated, but at least it works:

my_hash = {:x => 333, :y => 13, :z => [1,2,{:zz => [40,50]},[10,20]], :a => {:o => "1", :p => "2"}}


# Create Recursive function to get values:
def advance_hash_flattener(input, parent=[])
  case input
    when Hash then input.flat_map{|key, val|
      advance_hash_flattener(val, parent+[key])}
    when Array then input.flat_map{|x| advance_hash_flattener(x, parent)}
    else [parent.join('_>'), input]
  end
end

#Some small transformations for the last step:
first_step =  advance_hash_flattener(my_hash)
   .each_slice(2)
   .group_by{|x| x.first}
   .map{|x| [x.first, x.last.map(&:last)]}
p first_step #=> [["x", [333]], ["y", [13]], ["z", [1, 2, 10, 20]], ["z_>zz", [40, 50]], ["a_>o", ["1"]], ["a_>p", ["2"]]]

# Create an array of Hashes:
final_array = [Hash.new]
first_step.each do |key,values|
  new = []
  values.each do |val|
    if final_array.first.key?(key)
      final_copy = final_array.map{|x|x.clone}
      final_copy.each{|x| x[key] = val}
      new += final_copy
    else
      final_array.each{|x| x[key] = val}
    end
  end
  final_array += new
end
# result stored in final_array

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