Re: aggregate function for median calculation

I missed the first part, but if the numbers are rows in a table, why not
do something like:

numrows = select count(*) from table1 where some_condition
median_value = select some_col from table1 where some_condition order by
               some_col limit numrows/2, 1

(or something very close to that anyway).

-philip



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
>
>
>
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