Re: aggregate function for median calculation

On Mon, 18 Jun 2001, Alex Pilosov wrote:

> On Mon, 18 Jun 2001, Thalis A. Kalfigopoulos wrote:
>
> > Hippl,
> > I'm interested in calculating the median of a set of numbers.
> > The algorithm requires that all values are known in advance (ie stored
> > in an array). So the question is: how can I store everything first in
> > an array so I can later process it given that I'd like this to be an
> > aggregate function. I thought of creating an aggregate function and
> > have the state_function() gather all the values of a group in an array
> > and the final_function() to do the actuall median calculation on this
> > array. But the intermmediate state cannot hold multiple values in an
> > array (can it?) Any ideas on how to go with this?
>
> With current architecture, its kinda painful to implement such a function.
> Your 'state' function should allocate (palloc) memory for each element
> processed and then pfree it when you are done.
>
> -alex

So is there a way I can actually have a variable (the array with the elements) maintained between calls of the same function? I'm trying to figure how to design the aggregate's state_function that will do the element accumulation (before actually passing this array to the final to calculate the median).

TIA,
thalis