[ESS] setwd shortcut

[baptiste auguie]

Dear ESS gurus,

Quite often the first line of my R source code is to set the working
directory where the source file resides. On a Mac, to find the
filepath, I usually open a Terminal window and drag a folder from the
Finder. I then copy this path and paste it in the setwd("") command in
aquamacs. It's quite a convoluted process, a waste of time and focus.
I suddenly realized that it should be possible to do it within emacs
alone --- some magic C-c C-??? command that would return the filepath
of the buffer wrapped inside setwd("").

Any tips?

Regards,

baptiste