public function sum($sum=null)
    {
        $sum = LambdaUtils::toSelectCallable($sum);
        $temp = $this->select($sum)->toArray();
        return array_sum($temp);
    }
public function sum($sum=null)
    {
        $sum = LambdaUtils::toSelectCallable($sum);
        $temp = $this->select($sum)->toArray();
        return array_sum($temp);
    }
public function sum ( $ sum = null ) { $ sum = LambdaUtils :: toSelectCallable ( $ sum ) ; $ temp = $ this -> select ( $ sum ) -> toArray ( ) ; return array_sum ( $ temp ) ; }
Calculates the sum of values from given expression
@param callable|string|null $sum
@return numeric
Calculates the sum of values from given expression