adds tests

src/pg/sql/18_outliers.sql

@@ -12,6 +12,7 @@ END;
 $$ LANGUAGE plpgsql;
 
 -- Find outliers by a percentage above the threshold
+-- TODO: add symmetric option? `symmetric boolean DEFAULT false`
 
 CREATE OR REPLACE FUNCTION CDB_PercentOutlier(attr numeric[], outlier_fraction numeric, ids int[])
 RETURNS TABLE(outlier boolean, rowid int)
@@ -21,10 +22,15 @@ DECLARE
   out_vals boolean[];
 BEGIN
 
-  SELECT avg(i) INTO avg_val FROM unnest(attr) As x(i);
+  SELECT avg(i) INTO avg_val
+    FROM unnest(attr) As x(i);
 
-  SELECT array_agg( i > avg_val * outlier_fraction) INTO out_vals
-  FROM unnest(attr) As x(i);
+  SELECT array_agg(
+           CASE WHEN avg_val = 0 THEN null
+                ELSE  outlier_fraction > i / avg_val
+           END
+              ) INTO out_vals
+    FROM unnest(attr) As x(i);
 
   RETURN QUERY
   SELECT unnest(out_vals) As outlier,
@@ -45,10 +51,10 @@ DECLARE
 BEGIN
 
   SELECT stddev(i), avg(i) INTO stddev_val, avg_val
-  FROM unnest(attrs) As x(i);
+    FROM unnest(attrs) As x(i);
 
   SELECT array_agg(abs(i - avg_val) / stddev_val > num_deviations) INTO out_vals
-  FROM unnest(attrs) As x(i);
+    FROM unnest(attrs) As x(i);
 
 
   RETURN QUERY