Question

Is there a more Ruby-ish and cleaner way to get a number to operate within a range. If it hits the upper bound, the next number should be 1 again. Often seen in algorythms that e.g. force month 16 and 28 to be April (16-12=4).

The case: I have twelve images and N questions. Each question gets the next image, if all images are “used”, it should re-start at image 1.

def image_rotation(number) {
   uplim = 12

   return number if number <= uplim
   return image_rotation(number - uplim) if number > uplim
}

questions.each_with_index do |q,i|
  img = File::join("images", "image-#{image_rotation(i+1)}.jpg")
end

Note: I am not familiar with the terminology of this (kind of) problem, so searching stackoverflow did not give me any results or hints; but I cannot believe this question is not a duplicate, yet. Please point me to a keyword, answer/duplicate or feel free to answer it 🙂

And Bonuspoints for a one-liner. I need this in an ERB-file, so if I can keep the code clean, clear and simple, then I prefer to have it solved there, entirely.

Answer 1

Use modulo (%):

def image_rotation(number) do
   upper_limit = 12
   number % upper_limit
end

image_rotation(12) #=> 12
image_rotation(13) #=> 1

If that’s all your method does, though, you could just do:

i % 12