Move data.table to Imports:

[MichaelChirico]

Depends are discouraged for data.table:

Rdatatable/data.table#3076

(in fact, we hope that R will eventually deprecate this mode of dependency)

I used {lintr} to find all {data.table} usages in your package.

dt_exports <- getNamespaceExports("data.table")
dt_functions <- grep("^[a-zA-Z]", dt_exports, value=TRUE)
dt_operators <- grep("^[%]", dt_exports, value=TRUE)
lintr::lint_package(linters = list(
  lintr::undesirable_function_linter(setNames(nm = dt_functions)),
  lintr::undesirable_operator_linter(setNames(nm = dt_operators))
))

I added some qualifications of functions like melt() and first() that are also exported also by data.table to clarify their source, but could revert this if seen fit.

The qualifications in tests are needed as {data.table} is no longer attached for those.