Returning a sample set from a Mongoid collection.

mongoid_criteria.rb

module Mongoid
  class Criteria
    
    def sample(n = 1)
      indexes = (0..self.count-1).sort_by{ rand }.slice(0,n).collect!
      if n == 1
        return self.skip(indexes.first).first
      else
        return indexes.map{ |index| self.skip(index).first }
      end
    end

  end
end