On Tue, Mar 15, 2016 at 8:36 AM, David Fetter <david@fetter.org> wrote:
>
> Please find attached a patch that uses the float8 version to cover the
> numeric types.
Is there a well-defined meaning for having a negative weight? If no,
should it be disallowed?
I don't know what I was expecting, but not this:
select weighted_avg(x,10000000-2*x) from generate_series(1,10000000) f(x); weighted_avg
------------------16666671666717.1
Also, I think it might not give the correct answer even without
negative weights:
create table foo as select floor(random()*10000)::int val from
generate_series(1,10000000);
create table foo2 as select val, count(*) from foo group by val;
Shouldn't these then give the same result:
select stddev_samp(val) from foo; stddev_samp
-------------------2887.054977297105
select weighted_stddev_samp(val,count) from foo2;weighted_stddev_samp
---------------------- 2887.19919651336
The 5th digit seems too early to be seeing round-off error.
Cheers,
Jeff
