RE: [HACKERS] Standard Deviation function.

> I really need a Standard Deviation aggregate function...
> 
> I know about the man pages for "create aggregate" and "create
> function".  Is there something else I should look at?
> 
> It seems kind of hard to do with only two state functions unless
> I "cheat".  I need to keep three values, Count, Sum, and Sum of
> Squares.
> 
> Any hints or advice??

I thought about this a long time ago and had an idea but never
got around to trying to implement it.  I was going to have some
functions that worked on a structure of two doubles to track
the sum and square instead of using only one simple type.

darrenk