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Date: Mon, 11 Jan 2016 13:26:57 -0800
From: David Fetter <david@fetter.org>
To: Haribabu Kommi <kommi.haribabu@gmail.com>
Cc: Jim Nasby <Jim.Nasby@bluetreble.com>,
 PG Hackers <pgsql-hackers@postgresql.org>
Subject: Re: Weighted Stats
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On Fri, Jan 08, 2016 at 04:37:36PM +1100, Haribabu Kommi wrote:
> On Mon, Dec 21, 2015 at 1:50 PM, David Fetter <david@fetter.org> wrote:
> > On Sun, Dec 20, 2015 at 06:13:33PM -0600, Jim Nasby wrote:
> >> On 11/2/15 5:46 PM, David Fetter wrote:
> >> >I'd like to add weighted statistics to PostgreSQL
> >>
> >> Anything happen with this? If community isn't interested, ISTM it'd be good
> >> to put this in PGXN.
> >
> > I think it's already in PGXN as an extension, and I'll get another
> > version out this early this week, as it involves mostly adding some
> > tests.
> >
> > I'll do the float8 ones for core this week, too, and unless there's a
> > really great reason to do more data types on the first pass, it should
> > be in committable shape.
> 
> I reviewed the patch, following are my observations.
> 
> 1. +       precision</type>, <type>numeric</type>, or <type>interval</type>
> 
> with interval type it is giving problem. As interval data type is not supported,
> so remove it in the list of supported inputs.

I'd meant to add more, but will make sure that the next version
documents exactly the types it supports.

> postgres=# select weighted_avg(f7,f1) from tbl;
> ERROR:  function weighted_avg(interval, smallint) does not exist at character 8
> HINT:  No function matches the given name and argument types. You
> might need to add explicit type casts.
> 
> 
> 2. +float8_weighted_avg(PG_FUNCTION_ARGS)
> 
> It will be helpful, if you provide some information as a function header,
> how the weighted average is calculated similar like other weighted functions.

Will do.

> 3. + transvalues = check_float8_array(transarray,
> "float8_weighted_stddev_accum", 4);
> 
> The second parameter to check_float8_array should be "float8_weighted_accum".

Oops.  Will fix.

> 4. There is an OID conflict of 4066 with latest master code.

Will fix.

> 5.+ A += newvalW * ( newvalX - transvalues[2] ) / W;
> + CHECKFLOATVAL(A, isinf(newvalW) || isinf(newvalX - transvalues[2])
> || isinf(1.0/W), true);
> 
> + Q += newvalW * (newvalX - transvalues[2]) * (newvalX - A);
> + CHECKFLOATVAL(A, isinf(newvalX -  transvalues[3]) || isinf(newvalX -
> A) || isinf(1.0/W), true);
> 
> 
> Is the need of calculation also needs to be passed to CHECKFLOATVAL?
> Just passing
> the variables involved in the calculation isn't enough? If expressions
> are required then
> it should be something as follows?
> 
> CHECKFLOATVAL(A, isinf(transvalues[2]) || isinf(newvalW) ||
> isinf(newvalX - transvalues[2]) || isinf(1.0/W), true);
> 
> CHECKFLOATVAL(Q, isinf(transvalues[3]) || isinf(newvalX -
> transvalues[2]) || isinf(newvalX - A) || isinf(1.0/W), true);

Will fix.

> I verified the stddev transition and final function calculations
> according to wikipedia
> and they are fine.

Thanks for reviewing this!

Cheers,
David.
-- 
David Fetter <david@fetter.org> http://fetter.org/
Phone: +1 415 235 3778  AIM: dfetter666  Yahoo!: dfetter
Skype: davidfetter      XMPP: david.fetter@gmail.com

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