Re: how do you write aggregate function - Mailing list pgsql-general

From Martijn van Oosterhout
Subject Re: how do you write aggregate function
Date
Msg-id 20080311080345.GA17969@svana.org
Whole thread Raw
In response to Re: how do you write aggregate function  (Justin <justin@emproshunts.com>)
Responses Re: how do you write aggregate function
List pgsql-general
On Mon, Mar 10, 2008 at 10:01:47AM -0500, Justin wrote:
> i wish that could work  but need to keep track of the individual weights
> as its a percentage of the total amount of the weight.

Unless you have a different meaning of weighted average to me, I don't
think you do. AFAIK this would produce exactly the same result as what
your code does:

state_function(state,weight,value)
  state[0] = state[0]+weight
  state[1] = state[1]+weight*value

final_function(state)
  return state[1]/state[0]

The state[0] is the same as your _sumedWeight. Because it's a constant in
the second loop you can do the division after. state[1] is your
_sumedWxV times _sumedWeight.

Have a nice day,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Please line up in a tree and maintain the heap invariant while
> boarding. Thank you for flying nlogn airlines.

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