# File lib/utilities.rb, line 22
22:   def every(n, start = 0)
23:     select {|x| index(x) % n == start}
24:   end

    # File lib/utilities.rb, line 11
11:   def range
12:     self.max - self.min.to_f
13:   end

    # File lib/utilities.rb, line 15
15:   def sumup(column = nil, &block)
16:     self.inject(0) do |total, obj|
17:       value = column.nil? ? obj : obj.send(column)
18:       total += block.nil? ? value : yield(value)
19:     end
20:   end