Enumerable.average

Was looking around for a quickie function to do an average on an Enumerable/Array just like max and min - and found there isn't one. So here's a quick-n-dirty one that you can drop into config/environment.rb. Examples for use in the comments:

module Enumerable
  # returns a simple average of each item
  # If a block is passed - it will try to perform the operation on the item.
  # if the result is nil - it won't be counted towards the average.
  # Egs: 
  # [1,2,3].average == 2
  # ["a","ab","abc"].average &:length == 2
  # @purchases.average &:item_price == 10.45
  def average(&block)
    the_sum = 0
    total_count = 0
    self.each do |item|
      # either the actual item, or a method called on the item
      next_value = block_given? ? yield(item) : item
      unless next_value.nil?
        the_sum += next_value
        total_count += 1
      end
    end
    return nil unless total_count > 0
    the_sum / total_count
  end
end

I used it for displaying neat averages in the view thus:

    <p>Averages:
    <br />Number of items: <%= @purchases.average &:num_items -%>
    <br />Unit price: <%= @purchases.average &:price -%>
    <br />Total price: <%= @purchases.average {|p| p.num_items * p.price } -%> </p>