weighted_select.rb

# Returns a random item from a hash of key => weight
# -jodell 20100321  
def select_weighted(hsh)
  # roll randomly on the sum of values
  roll = rand(hsh.values.inject(0) { |sum, v| sum += v })  
  index = 0 
  hsh.each do |k, v|
    index += v
    return k if index > roll
  end 
end