To: pgsql-sql@postgresql.org
From: Seb <spluque@gmail.com>
Subject: creating a new aggregate function
Date: Mon, 03 Mar 2014 11:16:38 -0600
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Hi,

I'm trying to implement an aggregate function to calculate the average
angle from one or more angles and corresponding magnitudes.  So my first
step is to design a function that decomposes the angles and magnitudes
and returns the corresponding x and y vectors, and the following works
does this:

---<--------------------cut here---------------start------------------->---
CREATE OR REPLACE FUNCTION decompose_angle(IN angle numeric, IN magnitude numeric,
  OUT x numeric, OUT y numeric) RETURNS record AS
$BODY$
BEGIN
	x := sin(radians(angle)) * magnitude;
	y := cos(radians(angle)) * magnitude;
END;
$BODY$
  LANGUAGE plpgsql STABLE
  COST 100;
ALTER FUNCTION decompose_angle(numeric, numeric)
  OWNER TO sluque;
COMMENT ON FUNCTION decompose_angle(numeric, numeric) IS
  'Decompose an angle and magnitude into x and y vectors.';
---<--------------------cut here---------------end--------------------->---

Before moving on to writing the full aggregate, I'd appreciate any
suggestions to understand how to go about writing an aggregate for the
above, that would return the average x and y vectors.

Cheers,

-- 
Seb


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