reworking CDB_WeightedMean to be an aggregate function

src/pg/sql/11_kmeans.sql

@@ -8,24 +8,46 @@ RETURNS table (cartodb_id integer, cluster_no integer) as $$
 
 $$ language plpythonu;
 
-CREATE OR REPLACE FUNCTION CDB_WeightedMean(query text, weight_column text, category_column text default null )
+
-RETURNS table (the_geom geometry,class integer ) as $$
+CREATE OR REPLACE FUNCTION CDB_WeightedMeanS(state Numeric[],the_geom GEOMETRY(Point, 4326), weight NUMERIC)
+RETURNS Numeric[] AS 
+$$
+DECLARE 
+    newX NUMERIC;
+    newY NUMERIC;
+    newW NUMERIC;
 BEGIN
+    IF weight IS NULL OR the_geom IS NULL THEN 
+        newX = state[1];
+        newY = state[2];
+        newW = state[3];
+    ELSE
+        newX = state[1] + ST_X(the_geom)*weight;
+        newY = state[2] + ST_Y(the_geom)*weight;
+        newW = state[3] + weight;
+    END IF;
+    RETURN Array[newX,newY,newW];
 
-RETURN QUERY
-    EXECUTE format( $string$
-        select ST_SETSRID(st_makepoint(cx, cy),4326) the_geom, class  from (
-            select  
-                   %I as class,
-                   sum(st_x(the_geom)*%I)/sum(%I) cx,
-                   sum(st_y(the_geom)*%I)/sum(%I) cy
-                   from (%s) a
-                   group by %I
-            ) q          
-     
-        $string$, category_column, weight_column,weight_column,weight_column,weight_column,query, category_column 
-    )
-    using the_geom
-    RETURN;
 END
 $$ LANGUAGE plpgsql;
+
+CREATE OR REPLACE FUNCTION CDB_WeightedMeanF(state Numeric[])
+RETURNS GEOMETRY AS 
+$$
+BEGIN
+    IF state[3] = 0 THEN 
+        RETURN ST_SetSRID(ST_MakePoint(state[1],state[2]), 4326);
+    ELSE 
+        RETURN ST_SETSRID(ST_MakePoint(state[1]/state[3], state[2]/state[3]),4326);
+    END IF;
+END
+$$ LANGUAGE plpgsql;
+
+CREATE AGGREGATE CDB_WeightedMean(the_geom geometry(Point, 4326), weight NUMERIC)(
+    SFUNC = CDB_WeightedMeanS,
+    FINALFUNC = CDB_WeightedMeanF,
+    STYPE = Numeric[],
+    INITCOND = "{0.0,0.0,0.0}" 
+);
+
+

src/pg/test/expected/05_kmeans_test.out

@@ -4,7 +4,7 @@ SELECT count(DISTINCT cluster_no) as clusters from cdb_crankshaft.cdb_kmeans('se
 clusters
 2
 (1 row)
-SELECT count(*) clusters from cdb_crankshaft.cdb_WeightedMean( 'select *, code::INTEGER as cluster from ppoints' , 'value', 'cluster' );
+SELECT count(*) clusters from (select  cdb_crankshaft.CDB_WeightedMean(the_geom, value::NUMERIC), code from ppoints group by code) p;
 clusters
 52
 (1 row)

src/pg/test/sql/05_kmeans_test.sql

@@ -3,4 +3,4 @@
 
 SELECT count(DISTINCT cluster_no) as clusters from cdb_crankshaft.cdb_kmeans('select * from ppoints', 2);
 
-SELECT count(*) clusters from cdb_crankshaft.cdb_WeightedMean( 'select *, code::INTEGER as cluster from ppoints' , 'value', 'cluster' );
+SELECT count(*) clusters from (select  cdb_crankshaft.CDB_WeightedMean(the_geom, value::NUMERIC), code from ppoints group by code) p;