Hi all,

I'm running a multiplayer study on Prolific, and I've noticed a problem with random.shuffle. Somehow, the arrays that I randomize keep the same order for every session I run for an entire day. The arrays should randomize for each session I run, but if I run 5 or 6 sessions in a day, they all have the same exact "randomized" order. 

class C(BaseConstants):
    NAME_IN_URL = 'multiplayer_app'
    PLAYERS_PER_GROUP = 3
    NUM_ROUNDS = 150
    colors = ["red", "blue", "green", "yellow", "purple", "brown"]
  
    random.shuffle(colors)
    
    
for example..

say session 1 returns: colors = ["blue", "yellow", "red", "brown", "purple", "green"],

all other sessions I run that day (which are independent from this one) return the same exact 'randomized' sequence of colors.


Can anybody explain why this is, and a possible solution? Thanks.

Hi,

To implement a new randomisation in each session:

- Remove from class C() the line:
random.shuffle(colors)

- Define the following global function (outside of any class in your __init__.py file):

def creating_session(subsession: Subsession):
    if subsession.round_number == 1:
        session = subsession
        session.vars['colors'] = random.sample(C.colors, k=len(C.colors))
        
- Where you need it, retrieve the randomised list of colors using:
session = subsession

colors = session.vars['colors']

Best wishes

Thanks for the help. I am now getting "NameError: name 'subsession' is not defined" at the "session = subsession" line where I'm retrieving the list. Any ideas on why that is? I've never used subsession variables so I'm not sure where the issue is.

I assume that you are using a text editor (most probably, you would benefit enormously from using oTree Studio instead): 
- I left a typo, the line should read:
    
    session = subsession.session

- You would need to make sure that the function creating_session() is palced below the lines where the class Subsession() is defined.

I've tried session = subsession.session, and I'm still getting the error. And yes, creating_session() is below Subsession().


This is how I'm trying to access:

class Fixation(Page):
    form_model = 'player'
    timeout_seconds = 1

    @staticmethod
    def vars_for_template(player: Player):
        group = player.group

        session = subsession.session

        colors = session.vars['colors']

Apologies, I didn’t properly read your second post:
- when retrieving the session object, you need to start from player, group, or subsession;
- if you are in a method/function where you have access to the player object, as it is often the case, then you would do:

session = player.session

Ahh yes now it works. Thank you so much for your quick and extremely helpful responses!