[Rd] How to organized code in the R/ directory of a package?

[Peng Yu]

I'm making a package, Current, I put all R files in the R/ directory
in the package (without using subdirectory). This will become a
problem when there are many files in the directory. I'm wondering how
to use subdirectories in R/?

Does 'R CMD INSTALL' install the files in the subdirectories automatically?