Simple k-means example

kmeans.sql

-- Run against https://github.com/pramsey/postgis/tree/kmeans

CREATE TABLE g (id integer, g geometry);

INSERT INTO g
WITH r AS (
    SELECT random() u1, random() u2 FROM generate_series(1,10)
),
xy AS (
    SELECT a + sqrt(-2*ln(u1))*cos(2*pi()*u2) AS x,
           a + sqrt(-2*ln(u1))*sin(2*pi()*u2) AS y,
           a
    FROM r, generate_series(1,2) a
)
SELECT a, ST_MakePoint(x, y) g FROM xy;

SELECT ST_KMeans(g, 2) OVER (),ST_AsText(g),id FROM g;