On 07/17/2013 08:18 AM, Florian Lengyel wrote:
Is there a running median algorithm in PostGIS?
Hi Florian,
Unless I'm missing a spatial aspect to this question, this seems more
like a straight PostgreSQL question. The first issue is providing a
median() function. One common solution is to use PL/R [1]. Then, a
running median could be implemented with a window function [2]. The
general form (assuming the median aggregate function was already created
as in [1]) would be
SELECT median(column1) OVER (ORDER BY column2) FROM table1;
This would produce a running median, i.e., the median for the current
row and all previous rows given the sort order of the resultset. See in
particular the explanation of window frames and the use of the ORDER BY
clause in [2].
Best,
--Lee
[1] http://www.joeconway.com/plr/doc/plr-aggregate-funcs.html
[2] http://www.postgresql.org/docs/9.1/static/tutorial-window.html
--
Lee Hachadoorian
Assistant Professor in Geography, Dartmouth College
http://freecity.commons.gc.cuny.edu
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