In R, is there a way to know the path to the source file where a given function is defined?

I'm writing a unit test in R, which needs to read some test data defined in the 开发者_Go百科same directory. But I would also like to be able to run that unit test no matter what the current working directory happens to be.

Is there a way to tell R to load a file from here, where here is defined as the directory holding the source file of the function being executed?

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Depends on how what you mean with "I'm writing a unit test". If you just source that function from wherever, David is right and I don't even see the need to do that as you know which directory it is.

I would include that function in a package, and then there are mechanisms in R allowing you to make the data available for loading or via lazy-loading. See section 1.1.5 (Data in packages) in the manual Writing R Extensions. This is the R-way of doing it.

Another option Gabor Grothendieck gave in this thread on the R mailing list, is to add following line at the top of a script :

this.dir <- dirname(parent.frame(2)$ofile)

This will give the directory of the file when sourced using source(). Gabor calls it a dirty hack, and I agree with him.

On a sidenote, check also following packages for unit testing in R :

• RUnit
• svUnit
• testthat

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If the functions aren't in a package, and sourced from files via source() then perhaps source references might provide something to work with. Argument keep.source = TRUE is required, and read the R Journal article by Duncan Murdoch

Here is a quick example:

> setwd("./Downloads/")
> source("../foo.R", keep.source=TRUE) ## if options("keep.source") is FALSE
> bar
function(a, b) {
    a + b
}
> body(bar)
{
    a + b
}
attr(,"srcfile")
../foo.R 
attr(,"wholeSrcref")
bar <- function(a, b) {
    a + b
}

> srcref <- attr(body(bar), "srcref")[[1]]
> attr(srcref, "srcfile")
../foo.R
> ls(attr(srcref, "srcfile"))
[1] "Enc"       "encoding"  "filename"  "timestamp" "wd"       
> attr(srcref, "srcfile")$filename
[1] "../foo.R"
> attr(srcref, "srcfile")$wd
[1] "/home/gavin/Downloads"

Of course this assumes you don't know where the sourced functions come from to be of any use and yet the functions need to be sourced...

If this is in a package, then you can have data in a ./data directory or arbitrary directories in ./inst/. You can use data() toload datasets from the former, and system.file() for any file in a package. See the relevant help pages.

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There's no realistic hope of achieving this in full generality. Functions don't need to be loaded from files, they can be created dynamically by code, loaded from workspaces and so on.