Deep merge hashes. If both values are numeric they are summed. (Ruby)

README.md

Deep merge hashes. If both values are numeric they are summed.

$ ruby deep_sum_merge.rb
source:
layer_1: 10
deeper:
  layer_2: 20
  deeper:
    layer_3: 30
    deeper:
      some_text: im gonna get overwritten
      deeper:
        layer_5: 50

destination:
layer_1: 100
deeper:
  deeper:
    layer_3: 300
    deeper:
      layer_4: 400
      some_text: non-numerics are replaced as expected with Hash.merge
      deeper:
        layer_5: 500

merged result with sums:
layer_1: 110
deeper:
  layer_2: 20
  deeper:
    layer_3: 330
    deeper:
      some_text: non-numerics are replaced as expected with Hash.merge
      deeper:
        layer_5: 550
      layer_4: 400

It worked :)

The actual merge logic you are looking for here in the code below

deep_sum_merge.rb

require 'yaml'

source = {
  'layer_1' => 10,
  'deeper' => {
    'layer_2' => 20,
    'deeper' => {
      'layer_3' => 30,
      'deeper' => {
        'some_text' => 'im gonna get overwritten',
        'deeper' => {
          'layer_5' => 50
        }
      }
    }
  }
}

destination = {
  'layer_1' => 100,
  'deeper' => {
    'deeper' => {
      'layer_3' => 300,
      'deeper' => {
        'layer_4' => 400,
        'some_text' => 'non-numerics are replaced as expected with Hash.merge',
        'deeper' => {
          'layer_5' => 500
        }
      }
    }
  }
}

expected = {
  'layer_1' => 110,
  'deeper' => {
    'layer_2' => 20,
    'deeper' => {
      'layer_3' => 330,
      'deeper' => {
        'layer_4' => 400,
        'some_text' => 'non-numerics are replaced as expected with Hash.merge',
        'deeper' => {
          'layer_5' => 550
        }
      }
    }
  }
}

puts 'source:'
puts source.to_yaml.gsub(/^---\n/, '')
puts
puts 'destination:'
puts destination.to_yaml.gsub(/^---\n/, '')
puts

# store the merge logic
# http://ruby-doc.org/core-2.2.3/Hash.html#method-i-merge
def sum_merge(_, oldval, newval)
  if oldval.is_a?(Hash) && newval.is_a?(Hash)
    newval.merge!(oldval) { |_, oldval, newval| sum_merge(_, oldval, newval) }
  elsif oldval.is_a?(Numeric) && newval.is_a?(Numeric)
    oldval + newval
  else
    newval
  end
end

# use it
destination.merge!(source) { |_, oldval, newval| sum_merge(_, oldval, newval) }

puts 'merged result with sums:'
puts destination.to_yaml.gsub(/^---\n/, '')
puts

puts destination == expected ? 'It worked :)' : 'It did not work :('