Cumulative merge- a non destructive ruby merge operation

cumulative_merge.rb

# rather than blindly overwriting key=>value pairs in the target
# as #merge method, for each matching key found in the target, the 
# values are merged, meaning you can add to any level of the hash by 
# passing the full key=>value path to the value you wish to add to
def cumulative_merge(target, hash)
  if target.keys.include? hash.keys.first
    Hash[hash.keys.first, cumulative_merge(target[hash.keys.first], hash[hash.keys.first])]
  else
    target.merge(hash)
  end
end