Adding element to array that may not yet exist

gistfile1.rb

# Given:

hash = {}
(('a'..'z').to_a+('a'..'z').to_a).shuffle.each do |e|
  # represent the following two lines as a one-liner  
  hash[:"#{e}"] ||= []
  hash[:"#{e}"] << rand(10)
end

# one-liner for the two-liner above

(hash[e.to_sym] ||= []) << rand(10)