Ruby median

Was trawling through the google analytics search keywords and noticed somebody was looking for an Enumerable#median method when they came to this site. Got me thinking...

I went googling for solutions and found that some of them were just plain wrong... can't have that.

module Enumerable
  def median
    # trivial cases
    return nil if self.empty?

    mid = self.length / 2
    if self.length.odd?
      (entries.sort)[mid]
    else
      s = entries.sort
      (s[mid-1] + s[mid]).to_f / 2.0
    end
  end
end

This one isn't the most time-efficient (the sort can get long). I'd need to implement the selection-algorithm for the most optimal solution... but it'll do for a quick fix. I'll post again here if I get around to the better one.