I have created a report based on a CSV data source. This data source has two columns where there is one field called 'Quantity'. In the report, I have a text box item which displays the sum of the quantity where I need to take the sum of the CSV data source 'Quantity' field. I can not configure the data source to send the sum of the quantities beforehand so I need to do this sum in the rendering process of the report. Is there a function where I can achieve this?