Matching based on priorities

pages.py

class GroupingWaitPage(WaitPage):
    _allow_custom_attributes = True
    group_by_arrival_time = True

    def get_unique(self, wp, priority, filtering=None, matched=None):
        seen = set()
        # we don't need to re-use matched players
        if matched:
            wp = [w for w in wp if w not in matched]
        # we need to filter the waiting players if we want to get rid of the priorities used in some other list
        if filtering:
            wp = [w for w in wp if w.participant.vars[priority] not in filtering]
        uniques = [p for p in wp if
                   p.participant.vars[priority] not in seen and not seen.add(p.participant.vars[priority])]
        return uniques

    def get_players_for_group(self, waiting_players):
        group_size = 3
        stopper = 6  # when the number of waiting players reach a certain threshold we start grouping them based on
        # their non-first priorities.
        # The next line just a naive break if there are no one to wait for anymore: then we match them randomly.
        slowpokes = [p for p in self.session.get_participants() if p._index_in_pages < self._index_in_pages]
        if len(slowpokes) == 0 and len(waiting_players) >= group_size:
            return waiting_players[:group_size]

        unique_1 = self.get_unique(waiting_players, 'first')
        if len(unique_1) >= group_size:
            return unique_1[:group_size]

        if len(waiting_players) >= stopper:
            # we need to find the lacking element in the second priorites to add missing one(s) to a first priority list
            priorities_1 = [w.participant.vars['first'] for w in unique_1]
            unique_2 = self.get_unique(waiting_players, 'second', filtering=priorities_1, matched=unique_1)
            unique_1_2 = unique_1 + unique_2
            if len(unique_1_2) >= group_size:
                return unique_1_2[:group_size]
            priorities_2 = [w.participant.vars['second'] for w in unique_2]
            unique_1_2_3 = unique_1_2 + self.get_unique(waiting_players, 'third', filtering=priorities_1 + priorities_2,
                                                        matched=unique_1_2)
            return unique_1_2_3[:group_size]

It is built on the assumption that:

1. Number of priorities equals 3.

2. Each member in the group should ideally have a unique top priority. If something more complicated need (like 2 journalists, 1 economist), the code needs adjustment