Of course, avg() is already in the spec, so this isn't the 'perfect' instance,
You can easily maintain an average as you see each row at the cost
of more divisions. (eg for the 9th item add one ninth of the difference between the item and the running average to the average).
Calculating a median value is something you can't do to the end (or more accurately I can't think of a way of doing any work until you have all the values).
Roger
