Execute a set of lines from another R file

Question

I'm not sure if this is even possible, but I'm looking for something similar to defining regions in R script. I would like to execute a pre-specified set of lines from another R script. I know I can run the entire file using source(filename) but instead of running the entire file, I would like to only run a few lines in the file.

Is it possible for me to define regions or anything similar in the file and then execute it from another file?

Any help would be much appreciated.

Answer 1

If you're worried about the region of interest will be shifted once you add new lines upstream, then an alternative (or slightly modified) version of MrFlick's answer would be read as:

sourcePartial <- function(fn,startTag='#from here',endTag='#to here') {
  lines <- scan(fn, what=character(), sep="\n", quiet=TRUE)
  st<-grep(startTag,lines)
  en<-grep(endTag,lines)
  tc <- textConnection(lines[(st+1):(en-1)])
  source(tc)
  close(tc)
}

Now you need to put a small, unique hash tag just above and below of the region of interest. Such as "#from here" and "#to here"

Answer 2

This doesn't sound like a super-safe idea given how easily line numbers can change during edits. Seems like it would be safest to split up your larger sourced file into smaller parts that are safer to include and run. But you could do something like this

sourcePartial <- function(fn, skip=0, n=-1) {
    lines <- scan(fn, what=character(), sep="\n", skip=skip, n=n, quiet=TRUE)
    tc <- textConnection(lines)
    source(tc)
    close(tc)
}

here we use scan() to read lines from a file. See the documentation for skip= and n= at ?scan to see how to skip a certain number of lines and stop reading after a certain number. So

sourcePartial("test.R", 4, 11)

would run lines 5-15 from "test.R"