add method to Integer to choice integers like array#sample

sample_integers.rb

class Integer
  def sample(num = 1)
    to_a.sample(num)
  end
  
  def to_a
    @to_a ||= self.times.map{|i| i + 1}
  end
end


#
# 10.sample(2) 
# #=> [5, 1]
#
# * choice integers from [1, 2, ... n] 
# * sampled integers are unique
# 
# it make easy to generate mock like that
# 100.times do
#   article = article.new(...)
#   100.sample(10).each do |tag_id|
#     article.tag_ids << tag_id
#   end
# end
#