added CDB_Math_mode

NEWS

@@ -1,3 +1,7 @@
+0.3.X (2014-XX-XX)
+------------------
+Added CDB_Math_Mode function
+
 0.3.6 (2014-08-11)
 ------------------
 Dummy release to solve some issues with cdb branch/tag

scripts-available/CDB_Math.sql

@@ -0,0 +1,26 @@
+-- CartoDB Math SQL functions
+
+
+-- Mode
+-- https://wiki.postgresql.org/wiki/Aggregate_Mode
+
+CREATE OR REPLACE FUNCTION cartodb._CDB_Math_final_mode(anyarray)
+  RETURNS anyelement AS
+$BODY$
+    SELECT a
+    FROM unnest($1) a
+    GROUP BY 1 
+    ORDER BY COUNT(1) DESC, 1
+    LIMIT 1;
+$BODY$
+LANGUAGE 'sql' IMMUTABLE;
+
+DROP AGGREGATE IF EXISTS cartodb.CDB_Math_Mode(anyelement);
+
+CREATE AGGREGATE cartodb.CDB_Math_Mode(anyelement) (
+  SFUNC=array_append,
+  STYPE=anyarray,
+  FINALFUNC=_CDB_Math_final_mode,
+  INITCOND='{}'
+);
+

scripts-enabled/220-CDB_Math.sql

@@ -0,0 +1 @@
+../scripts-available/CDB_Math.sql

test/CDB_MathTest.sql

@@ -0,0 +1,4 @@
+
+SELECT cdb_math_mode(a) from unnest(ARRAY[1,2,2,3]) a;
+SELECT cdb_math_mode(a) from unnest(ARRAY[1,2,3]) a;
+SELECT cdb_math_mode(a) from unnest(ARRAY[1]) a;

test/CDB_MathTest_expect

@@ -0,0 +1,3 @@
+2
+1
+1