http://ruby.railstutorial.org/chapters/rails-flavored-ruby?version=4.0#sec-exercises Exercise 4.6

4_6_1.rb

def string_shuffle(s)
  s.split('').shuffle.join
end

p string_shuffle("foobar")

4_6_2.rb

class String
  def shuffle
    self.split('').shuffle.join
  end
end

p "foobar".shuffle

4_6_3.rb

params = Hash.new
params[:father] = Hash.new
params[:father][:first] = "Takahiro"
params[:father][:last] = "Okumura"

params[:mother] = Hash.new
params[:mother][:first] = "Haha"
params[:mother][:last] = "Okumura"

params[:child] = Hash.new
params[:child][:first] = "Chichi"
params[:child][:last] = "Okumura"

p params

4_6_4.rb

# Hash-merge
# http://ruby-doc.org/core-2.0/Hash.html#method-i-merge

params1 = {name: "Takahiro Okumura", email: "hfm@paperboy.co.jp"}
params2 = {job: "Engineer"}

p params1.merge(params2)
p params2.merge(params1)

4_6_3.rbは https://gist.github.com/kitak/5640738 が良さそう。