Calculate power set from an array

power_set.rb

arr = [1, 2, 3]
# => [1, 2, 3]

def power_set(arr)
   result = [[]]
   
   arr.each do |element|
     result += result.map do |num|
       num + [element]
     end
   end
   
   result
end
# => :power_set

power_set(arr)
# => [[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3]]

class Array
   def power_set
    total = [[]]
     self.each do |element|
      total += total.map do |num|
         num += [element]
       end
     end
     total
   end
end

[1, 2, 3].power_set
# => [[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3]]