http://forrst.com/posts/Turn_a_Nested_Ruby_Hash_into_a_One_dimensional_h-zaG

hash one dimensional.rb

# check the comments for @billmann's awesome solution to the same problem

def make_hash_one_dimensional(input = {}, output = {}, options = {})
  input.each do |key, value|
    key = options[:prefix].nil? ? "#{key}" : "#{options[:prefix]}#{options[:delimiter]||"_"}#{key}"
    if value.is_a? Hash
      make_hash_one_dimensional(value, output, :prefix => key, :delimiter => "_")
    else
      output[key]  = value
    end
  end
  output
end

nested_hash = {:a => {:b => {:c => {:d => {:e => "hi"}}}}, :f => "there"}
make_hash_one_dimensional(nested_hash)
#=> {"f"=>"there", "a_b_c_d_e"=>"hi"}