Fix evaluate average UDF

Author: Mahmoud Hanafy

src/main/java/com/highperformancespark/examples/dataframe/JavaUDFs.java

@@ -64,7 +64,7 @@ public void merge(MutableAggregationBuffer buffer1, Row buffer2) {
 
       @Override
       public Object evaluate(Row buffer) {
-        return Math.pow(buffer.getDouble(1), 1.0 / buffer.getLong(0));
+        return buffer.getDouble(1) / buffer.getLong(0);
       }
     }
 

src/main/scala/com/high-performance-spark-examples/dataframe/UDFs.scala

@@ -47,7 +47,7 @@ object UDFs {
       }
 
       def evaluate(buffer: Row): Any = {
-        math.pow(buffer.getDouble(1), 1.toDouble / buffer.getLong(0))
+        buffer.getDouble(1) / buffer.getLong(0)
       }
     }
     // Optionally register