Pick an array of numbers at random in oTree

Question

I'm trying to generate a random array of numbers. There are x rounds in my experiment. I want that a different picture is displayed in each round and that the pictures appear in a random order. I'm trying to embed some python code in models.py in order to do that but I'm not getting anywhere.

Answer 1

ok, let's say you have a set of images named 'img1.jpg, img2.jpg, img3.jpg' and so on - and for the simplicity let's assume that the number of such images coincides with your number of rounds.

a bit naïve but workable way of doing this is the following:

in models.py:

import random 
class Constants(BaseConstants):
    imgs = ['img1.jpg', 'img2.jpg', 'img3.jpg',]

class Subsession(BaseSubsession):
    def creating_session(self):
       if self.round_number == 1:
          for p in self.session.get_participants():
              imgs = Constants.imgs.copy()
              random.shuffle(imgs) 
              p.vars['images'] = imgs

in pages.py:

class MyPage(Page):
      def vars_for_template(self):
          image = self.participant.vars['images'][self.round_number - 1]
          return {'img_to_show': image}

that's it: you have an individual randomized image to show in each round for each participant, which you can later on use on a template for this page

PS: I called this approach naive because a slightly more sophisticated way of doing it would be to access the folder where the images are stored and get a subset of them that corresponds to the number of rounds in a game. But sometimes this direct approach is more error-prone.