Source only part of a file

Question

My R workflow is usually such that I have a file open into which I type R commands, and I’d like to execute those commands in a separately opened R shell.

The easiest way of doing this is to say source('the-file.r') inside R. However, this always reloads the whole file which may take considerable time if big amounts of data are processed. It also requires me to specify the filename again.

Ideally, I’d like to source only a specific line (or lines) from the file (I’m working on a terminal where copy&paste doesn’t work).

source doesn’t seem to offer this functionality. Is there another way of achieving this?

Answer 1

Here's another way with just R:

source2 <- function(file, start, end, ...) {
    file.lines <- scan(file, what=character(), skip=start-1, nlines=end-start+1, sep='\n')
    file.lines.collapsed <- paste(file.lines, collapse='\n')
    source(textConnection(file.lines.collapsed), ...)
}