Ordering a hash to xml: Rails

Question

I'm building an xml document from a hash. The xml attributes need to be in order. How can this be accomplished?

hash.to_xml

Answer 1

What order did you want them to be in? You shouldn't expect them to be in insertion order. From the docs for Hash:

The order in which you traverse a hash by either key or value may seem arbitrary, and will generally not be in the insertion order.

If you need them to be in a specific order you can determine just from the keys/values (e.g. order the attribute names alphabetically), you'll need to apply that ordering explicitly.

Answer 2

The usual ways of sorting a hash is by key or value. Have a look here:

hash.sort

More complex sorts can be accomplised however by utilizing the spaceship operator

Answer 3

h = Hash[:x,123,:a,553,:d,949,:e,5321]
=> {:e=>5321, :x=>123, :a=>553, :d=>949}
h.sort { |x,y| x[0].to_s <=> y[0].to_s }
=> [[:a, 553], [:d, 949], [:e, 5321], [:x, 123]]

Answer 4

Ruby 1.8's hash aren't in insertion order. With ruby 1.9, they will be.

However rails offers an alternative to that, the class OrderedHash.

my_hash = ActiveSupport::OrderedHash.new
my_hash[:key] = 'value'
my_hash[:second_key] = 'second value'

This hash is in fact an array of that format :

[[:key, 'value'], [:second_key, 'second value']]

The entries remains in the order you inserted them.
And you can access them like with any other hash.

Answer 5

This piece of code I've just made for i18n-js might help you out as it convert Hash to ActiveSupport::OrderedHash if needed then sort it's key by natural order.

http://seb.box.re/2010/1/15/deep-hash-ordering-with-ruby-1-8