LyX and Sweave: reading data files

[Jean-Marc Lasgouttes]

Hello there,

I am trying to use Sweave and LyX for a project of my own, and have the
following problem: my R code reads some data
  somevars<-read.table("somevars.dat")
and this data file is not available when Sweave is ran from the /tmp
directory. 

I guess this problem is quite common... How do people solve it in
general? I do not want to use an absolute path, since it makes the file
non portable...

JMarc