Merge pull request #81 from CartoDB/equalint

adding equal interval function for consistency

scripts-available/CDB_EqualIntervalBins.sql

@@ -0,0 +1,37 @@
+--
+-- Calculate the equal interval bins for a given column
+--
+-- @param in_array A numeric array of numbers to determine the best
+--                   to determine the bin boundary
+--
+-- @param breaks The number of bins you want to find.
+--  
+--
+-- Returns: upper edges of bins
+-- 
+--
+
+CREATE OR REPLACE FUNCTION CDB_EqualIntervalBins ( in_array NUMERIC[], breaks INT ) RETURNS NUMERIC[] as $$
+DECLARE 
+    diff numeric;
+    min_val numeric;
+    max_val numeric;
+    tmp_val numeric;
+    i INT := 1;
+    reply numeric[];
+BEGIN
+    SELECT min(e), max(e) INTO min_val, max_val FROM ( SELECT unnest(in_array) e ) x WHERE e IS NOT NULL;
+    diff = (max_val - min_val) / breaks::numeric;
+    LOOP
+        IF i < breaks THEN
+            tmp_val = min_val + i::numeric * diff;
+            reply = array_append(reply, tmp_val);
+            i := i+1;
+        ELSE
+            reply = array_append(reply, max_val);
+            EXIT;
+        END IF;
+    END LOOP;
+    RETURN reply;
+END;
+$$ language plpgsql IMMUTABLE;

scripts-enabled/240-CDB_EqualIntervalBins.sql

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

test/CDB_EqualIntervalBinsTest.sql

@@ -0,0 +1,5 @@
+WITH data AS (
+    SELECT array_agg(x::numeric) s FROM generate_series(1,300) x 
+        WHERE x % 5 != 0 AND x % 7 != 0
+    ) 
+SELECT round(unnest(CDB_EqualIntervalBins(s, 7)),7) FROM data

test/CDB_EqualIntervalBinsTest_expect

@@ -0,0 +1,7 @@
+43.5714286
+86.1428571
+128.7142857
+171.2857143
+213.8571429
+256.4285714
+299.0000000