How can I shuffle an array/hash in Ruby?

For learning purposes, what is this called? Is the object being created an array or a hash?

stack_of_cards = []

This is how I'm filling it:

stack_of_cards << Card.new("A", "Spades", 1)
stack_of_cards << Card.new("2", "Spades", 2)
stack_of_cards << Card.new("3", "Spades", 3)
...

Here is my Card class:

class Card

  attr_accessor :number, :suit, :value

  def initialize(number, suit, value)
    @number = number
    @suit = suit
    @value = value
  end

  def to_s
    "#{@number} of #{@suit}"
  end
end

I'd like to shuffle the elements in this array/hash (what is this called? :S)

Any suggestions?