public function sortByCount(string $expression) : Stage\SortByCount
    {
        $stage = new Stage\SortByCount($this, $expression, $this->dm, $this->class);
        $this->addStage($stage);

        return $stage;
    }
public function sortByCount(string $expression) : Stage\SortByCount
    {
        $stage = new Stage\SortByCount($this, $expression, $this->dm, $this->class);
        $this->addStage($stage);

        return $stage;
    }
public function sortByCount ( string $ expression ) : Stage \ SortByCount { $ stage = new Stage \ SortByCount ( $ this , $ expression , $ this -> dm , $ this -> class ) ; $ this -> addStage ( $ stage ) ; return $ stage ; }
Groups incoming documents based on the value of a specified expression,
then computes the count of documents in each distinct group.

@see http://docs.mongodb.org/manual/reference/operator/aggregation/sortByCount/
Groups incoming documents based on the value of a specified expression then computes the count of documents in each distinct group .