Payout Algorithm Ruby - ruby-on-rails

Question

Im building a rails app that has users and scores. I want the top half of the users to get paid out. I have a separate tiebreaker input stored for each user if they get happen to tie for last place (last paid out place). For example, I need help, if their are 8 users and 4th and 5th tie in points. Then it calls my tiebreaker.
This is what I have tried:
First I am counting the users and determening the top half of the players:
theUsersCount = ParticipatingUser.where(game_id: game_id).size
numofWinners = theUsersCount / 2
Then I am taking the users and their scores and pushing it to an array then only showing the top half of the users that won.
userscores.push("#{user.username}" => playerScore})
userscores[0..numofWinners].sort_by { |y| y[:score] }
But I am unsure of how to take execute the tiebreaker if their is a tie for last place.

Answer 1

To get the users count you should use count rather than size - size fetches all the rows, then counts them, while count counts the rows in the DB, and returns the number:
user_count = ParticipatingUser.where(game_id: game_id).count
(actually - the above is wrong - here is an explanation - you should use size which smartly chooses between length and count - thanks #nzifnab)
Now, find the score of the user in the user_count/2 place
minimal_score = ParticipatingUser.order(:score, :desc).pluck(:score).take(user_count/2).last
And take all the users with this score or more:
winning_users = ParticipatingUser.where('score >= ?', minimal_score).order(:score, :desc)
now check if there are more users than expected:
if winning_users.size > user_count/2
then break your ties:
tie_breaker(winning_users[user_count/2-1..-1])
All together:
user_count = ParticipatingUser.where(game_id: game_id).size
minimal_score = ParticipatingUser.order(:score, :desc).pluck(:score).take(user_count/2).last
winning_users = ParticipatingUser.where('score >= ?', minimal_score).order(:score, :desc)
if winning_users.size > user_count/2
losers = tie_breaker(winning_users[user_count/2-1..-1])
winning_users -= losers
end
winning_users