data.table conversion script question...

Have you checked out the vignettes for data.table? You can view them on the package's CRAN page. Especially Introduction to data.table.

Right now, we don't really have enough info to help you out. Could you ask this with a minimal REPRoducible EXample (reprex)? A reprex makes it much easier for others to understand your issue and figure out how to help.

If you've never heard of a reprex before, you might want to start by reading this FAQ: