Grouping large data

Hi all,

I'm connected to a large dataset (.txt 600 MB) hosted on a sharepoint. As I do not need all details in the dataset, I am grouping the data to make it smaller. However... I'm questionning "is this the right approach?" as the grouping step is quite heavy in terms of performance.

Overall, is it worth doing many steps in the "transform data" part given it's quite heavy and weight on performance? Or is it better to leave the data as raw as possible and manage as much as possible in the report part?

thanks

WY