Hello, 

I know this was somewhat addressed in a previous forum post, but I was hoping for a bit more guidance as this function is not working for me. I am trying to match participants in groups of 2, and each round they are matched with a participant they have not matched with before. I have tried setting the group matrix and the group by arrival time method but I am stumped.

Thanks for your help,
Ally

Hi,
The code below is for version 3.x of oTree but it can easily be modified to fit version 5.

---------------------------------------------
pairs = None


class Constants(BaseConstants):
    name_in_url = 'test'
    players_per_group = None


class Subsession(BaseSubsession):
     def creating_session(self):
        global pairs

        if self.round_number == 1:
            nb_participants = len(self.get_players())
            left_players = [p for p in self.get_players()[: nb_participants // 2]]
            right_players = [p for p in self.get_players()[nb_participants // 2:]]
            pairs = self.get_pairs(left_players, right_players)

        self.set_group_matrix(next(pairs))

    def get_pairs(self, left_players, right_players):
        left = [p.id_in_subsession for p in left_players]
        right = [p.id_in_subsession for p in right_players]

        while True:
            yield list(map(list, zip(left, right)))
            right.append(left.pop())
            left.insert(1, right.pop(0))

-------------------

Best

Dimitri