hashmap - How to merge Ruby hashes

Question

How can I merge these two hashes:

{:car => {:color => "red"}}
{:car => {:speed => "100mph"}}

To get:

{:car => {:color => "red", :speed => "100mph"}}

Answer 1

There is a Hash#merge method:

ruby-1.9.2 > a = {:car => {:color => "red"}}
 => {:car=>{:color=>"red"}} 
ruby-1.9.2 > b = {:car => {:speed => "100mph"}}
 => {:car=>{:speed=>"100mph"}} 
ruby-1.9.2 > a.merge(b) {|key, a_val, b_val| a_val.merge b_val }
 => {:car=>{:color=>"red", :speed=>"100mph"}} 

You can create a recursive method if you need to merge nested hashes:

def merge_recursively(a, b)
  a.merge(b) {|key, a_item, b_item| merge_recursively(a_item, b_item) }
end

ruby-1.9.2 > merge_recursively(a,b)
 => {:car=>{:color=>"red", :speed=>"100mph"}}