How to use Rstudio relative paths

You could change the working directory. Get the address in the beginning getwd(), replace it by your project folder with setwd(). Then, when accessing a file just use read.table("./folder/file.R").

The so-called here package is really useful for avoiding absolute paths in (as well as outside of) RStudio. Suppose you have an RStudio project and want to access the file /data/file.txt. This would be done as follows. This way, you don't have to mess around with getwd(), just work relative to your project root using here().

library(here)
#> here() starts at C:/test/someproject
here("data", "file.txt")
#> "C:/test/someproject/data/file.txt"
readLines(here("data", "file.txt"))
#> "The here package is awesome!"

How here figures out where your project root is is described in ?here and also in the "Ode to the here package" by Jenny Bryan.