How do I add a prefix to each key in a hash?

Question

I have the following keys in my hash:

address, postcode

I want to add the "shipping_" prefix to each of them so they would become:

shipping_address, shipping_postcode

instead. How can I do this?

Answer 1

hsh1 = {'address' => "foo", 'postcode' => "bar"}
hsh2 = Hash[hsh1.map{|k,v| [k.dup.prepend("shipping_"),v]}]
p hsh2
# >> {"shipping_address"=>"foo", "shipping_postcode"=>"bar"}

update

hsh1 = {'address' => "foo", 'postcode' => "bar"}
hsh2 = Hash[hsh1.map{|k,v| ["shipping_#{k}",v]}]
p hsh2
# >> {"shipping_address"=>"foo", "shipping_postcode"=>"bar"}

Answer 2

In Ruby >= 2.5, you can do

hsh.transform_keys! {|k| 'shipping_' + k }
# => {"shipping_address"=>"foo", "shipping_postcode"=>"bar"} 

And if you want to be fancy

hsh.transform_keys! &'shipping_'.method(:+)
# => {"shipping_address"=>"foo", "shipping_postcode"=>"bar"}