Re: how do you write aggregate function

>>A couple of email pointers:
>>
>>* Please don't use language like "the Array would suck this bad" in
>>lists. I swear like a sailor in person, but it reads *very* badly in
>>email. There are a lot of people on this list who might take offense,
>>since it is their hard work that means that arrays work at all for
>>you...

That comment was not meant to be an insult or disparaging in any way
what so ever. If it was taken as such then i'm sorry.

It seems the biggest performance hit is copying of the array content
from one memory variable to another which is happening allot.

I'm not really against using a temp tables to hold onto values. I used
to do that in Foxpro when i hit the hard limit on its array but other
problems start popping up. If we use a temp table keeping track what
going with other users can make life fun.

I really want to figure this out how to speed it up. I have to write
allot more aggregate functions to analyze R&D data which will happen
latter this year. right now this function will be used in calculating
manufacturing cost.

Webb Sprague wrote:
> A couple of email pointers:
>
> * Please don't use language like "the Array would suck this bad" in
> lists. I swear like a sailor in person, but it reads *very* badly in
> email. There are a lot of people on this list who might take offense,
> since it is their hard work that means that arrays work at all for
> you...
>
> * Please don't topquote.
>
> On Mon, Mar 10, 2008 at 8:01 AM, Justin <justin(at)emproshunts(dot)com> 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.
>>
>
> The definition of "weighted mean" doesn't require that the weights be
> normalized. You probably need to calculate this separately, either
> using a temp table or a column in the original table.
>
>
>> I would never have thought the performance of the Array would suck this
>> bad.
>>
>
> You should be using a temp table or a new column as above to store the
> normalized weights, and then calling the original aggregate on those.
> (a) calculate sum of weights (aggregate), (b) calculate normalized
> weight for each row (weight / total), (c) find weighted mean with
> aggregate that retains only the totals between function calls. If you
> let your arrays grow to the size of tables, performance will suffer
> (as they are not meant to do that anyway). I don't think you can
> avoid two passes, whether inside a function or outside.
>
>
>> Martijn van Oosterhout wrote:
>> On Sun, Mar 09, 2008 at 11:40:47AM -0500, Justin wrote:
>>
>>
>> I got the aggregate function for weighted average done. I finely left
>> alone for more than 10 minutes to actual get it written. It takes 2
>> value input Weight and the Value. it will sum the weighted entries to
>> create the constant then does the normal formula, but does not
>> percentage number but averaged number. A simple change on the return
>> line it can do percentages.
>>
>> If you're looking for performance, ISTM the best option would be to
>> simply accumulate the weights and value*weight as you go and do a
>> division at the end. That seems likely to beat any implementation
>> involving array_append.
>>
>> Have a nice day,
>>
>>
>>