[R] constructing a relative path

[Mark Heckmann]

Dear R-users,

I want to construct a relative path in R, but I am not able to do it or to
find a function that does it.
My solution is somewhat awkward as it uses string manipulation.

The problem: I have the following folder structure. 

project_folder
       |
       |----- data
       |----- scripts
       |----- output

My working directory is the scripts folder.
Now I want to construct a relative path to the data folder.

Is there an easy way or a function?

TIA

Mark