sql

lib/sql/scripts-available/CDB_HeadsTailsBins.sql

@@ -0,0 +1,46 @@
+--
+-- Determine the Heads/Tails classifications from a numeric array
+--
+-- @param in_array A numeric array of numbers to determine the best
+--            bins based on the Heads/Tails method.
+--
+-- @param breaks The number of bins you want to find.
+--  
+--
+
+CREATE OR REPLACE FUNCTION @extschema@.CDB_HeadsTailsBins ( in_array NUMERIC[], breaks INT) RETURNS NUMERIC[] as $$ 
+DECLARE 
+    element_count INT4; 
+    arr_mean numeric; 
+    i INT := 2; 
+    reply numeric[]; 
+BEGIN 
+    -- get the total size of our row
+    element_count := array_upper(in_array, 1) - array_lower(in_array, 1); 
+    -- ensure the ordering of in_array
+    SELECT array_agg(e) INTO in_array FROM (SELECT unnest(in_array) e ORDER BY e) x;
+    -- stop if no rows 
+    IF element_count IS NULL THEN  
+        RETURN NULL; 
+    END IF; 
+    -- stop if our breaks are more than our input array size
+    IF element_count < breaks THEN  
+        RETURN in_array; 
+    END IF; 
+
+    -- get our mean value
+    SELECT avg(v) INTO arr_mean FROM (  SELECT unnest(in_array) as v ) x; 
+
+    reply = Array[arr_mean];
+    -- slice our bread
+    LOOP  
+        IF i > breaks THEN  EXIT;  END IF;  
+        SELECT avg(e) INTO arr_mean FROM ( SELECT unnest(in_array) e) x WHERE e > reply[i-1];
+        IF arr_mean IS NOT NULL THEN
+            reply = array_append(reply, arr_mean);
+        END IF;
+        i := i+1; 
+    END LOOP; 
+    RETURN reply; 
+END; 
+$$ language plpgsql IMMUTABLE PARALLEL SAFE;