diff --git a/src/AggregationFunction/FunctionSum.php b/src/AggregationFunction/FunctionSum.php
index 3ef1cf80..e1b89513 100644
--- a/src/AggregationFunction/FunctionSum.php
+++ b/src/AggregationFunction/FunctionSum.php
@@ -8,23 +8,32 @@
 
 namespace Ublaboo\DataGrid\AggregationFunction;
 
-class FunctionSum implements IAggregationFunction
-{
+use DibiFluent;
+use Doctrine\ORM\QueryBuilder;
+use Nette\Utils\Strings;
 
+final class FunctionSum implements IAggregationFunction
+{
 	/**
 	 * @var string
 	 */
-	protected $column;
+	private $column;
 
 	/**
 	 * @var int
 	 */
-	protected $result = 0;
+	private $result = 0;
 
 	/**
 	 * @var int
 	 */
-	protected $dataType;
+	private $dataType;
+
+	/**
+	 * @var callable
+	 */
+	private $renderer;
+
 
 	/**
 	 * @param string $column
@@ -47,23 +56,25 @@ public function getFilterDataType()
 
 
 	/**
-	 * @param  mixed $data_source
+	 * @param  mixed  $dataSource
 	 * @return void
 	 */
-	public function processDataSource($data_source)
+	public function processDataSource($dataSource)
 	{
-		if ($data_source instanceof \DibiFluent) {
-			$connection = $data_source->getConnection();
+		if ($dataSource instanceof DibiFluent) {
+			$connection = $dataSource->getConnection();
 			$this->result = $connection->select('SUM(%n) AS sum', $this->column)
-				->from($data_source, 's')
+				->from($dataSource, 's')
 				->fetch()
 				->sum;
 		}
-		if ($data_source instanceof \Doctrine\ORM\QueryBuilder) {
-			$column = \Nette\Utils\Strings::contains($this->column, '.')
-				? $this->column 
-				: current($data_source->getRootAliases()).'.'.$this->column;
-			$this->result = $data_source
+
+		if ($dataSource instanceof QueryBuilder) {
+			$column = Strings::contains($this->column, '.')
+				? $this->column
+				: current($dataSource->getRootAliases()).'.'.$this->column;
+
+			$this->result = $dataSource
 				->select(sprintf('SUM(%s)', $column))
 				->getQuery()
 				->getSingleScalarResult();
@@ -72,11 +83,27 @@ public function processDataSource($data_source)
 
 
 	/**
-	 * @return int
+	 * @return mixed
 	 */
 	public function renderResult()
 	{
-		return $this->result;
+		$result = $this->result;
+
+		if (isset($this->renderer)) {
+			$result = call_user_func($this->renderer, $result);
+		}
+
+		return $result;
 	}
 
+
+	/**
+	 * @param  callable|NULL  $callback
+	 * @return static
+	 */
+	public function setRenderer(callable $callback = NULL)
+	{
+		$this->renderer = $callback;
+		return $this;
+	}
 }