When developing an R package, it has been suggested to just put the dependent packages in Description file under Imports section.

However, I recently found that for S3 methods exported by a package, one need to import such functions explicitly in order to use them in the developed package. One example is the unique() function from the package data.table. This function can’t be called via data.table::unique(), because it is a S3 method. However, if it is not imported, the method uniq.data.frame() would be used instead.

To import it, one can add the following roxygen2 comment above the calling function:

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#' @importFrom data.table unique

Then run devtools::document() to update relevant files, including NAMESPACE.

This is just a quick note in case similar problems are met in future.

😄

Happy Chinese Lunar New Year!