Question

Consider a class Team, with class variables ‘wins’ and ‘losses’. I wish to sort an array of Teams by the win:loss ratio, such that:

5:0 > 3:0 > 1:0 > 3:1 > 5:5 > 3:3 > 1:3 > 0:1 > 0:3 > 0:5

I already have a (partial) hacked together solution that I’m not happy with, and I’m wondering if there is a cleaner/more elegant/simpler way to solve this problem.

def ratio
    if @losses == 0 then 
        return 1000000+@wins
    end
    if @wins == 0 then
        return 0-@losses
    end
    return @wins/@losses
end

(This does not fix 5:5 > 3:3)

Which would be in the Team class and could be used like this:

teams.sort! { |a, b| b.ratio <=> a.ratio }

What is the simplest way to solve this? (Solutions does not have to be Ruby, I’m happy with anything that is OO)

Answer 1

I don’t speak Ruby, but a Python approach which would give your desired results would use a tuple for a key (in the decorate-sort-undecorate “Schwartzian transform” idiom.)

For example, you could rank by win fraction, then number of wins, then (negative) number of losses, which would give your desired ordering:

>>> wl = [[3, 0], [3, 1], [0, 5], [3, 3], [0, 3], [5, 5], [1, 3], [5, 0]]
>>> 
>>> def rank(wl):
...     win, loss = wl
...     return (1.0*win/(win+loss) if win+loss > 0 else 0), win, -loss
... 
>>> sorted(wl, key=rank)
[[0, 5], [0, 3], [1, 3], [3, 3], [5, 5], [3, 1], [3, 0], [5, 0]]
>>> sorted(wl, key=rank)[::-1]
[[5, 0], [3, 0], [3, 1], [5, 5], [3, 3], [1, 3], [0, 3], [0, 5]]

I don’t know what the Ruby equivalent is, unfortunately, but I gather that there’s a sort_by method floating around somewhere.