this.path

Description

this.path aims to provide a mechanism for retrieving the path of an R script within itself without needing to explicitly write its path elsewhere. Additionally, it provides a mechanism for specifying file paths against the executing script's directory (without changing the working directory).

Installation

Install it from CRAN:

install.packages("this.path")

Install the development version from GitHub:

install.packages("this.path", repos = "https://raw.githubusercontent.com/ArcadeAntics/PACKAGES")

Details

The most important functions from this.path are this.path(), this.dir(), and here().

this.path() returns the normalized path of the executing script.

this.dir() return the normalized path of the directory in which the executing script is located.

here() constructs file paths against the executing script's directory.

this.path also provides functions for constructing and manipulating file paths. path.join(), basename2(), and dirname2() are drop in replacements for file.path(), basename(), and dirname() which better handle drives and network shares. splitext(), removeext(), ext(), and ext<-() split a path into root and extension, remove a file extension, get an extension, or set an extension for a file path.

this.path vs whereami

The only equivalent to this.path() (that I've seen) is whereami::thisfile(). R package whereami has many issues that this.path resolves:

1. this.path() works with sys.source(), debugSource() in RStudio, testthat::source_file(), and knitr::knit(). It also works in interactive mode inside RStudio, VSCode, and Rgui for Windows.

2. Related to source(), this.path():

   2.1. takes argument chdir into account.

   2.2. recognizes that file = "", file = "clipboard", and file = "stdin" are not opening files and skips them.

   2.3. accounts for file being a URL path.

   2.4. accounts for file being a connection instead of a character string.

   2.5. skips calls in which file is missing and exprs is used instead.

3. if an R script is being run from a shell, this.path() does a better job of extracting the command line argument -f FILE or --file=FILE.

4. this.path() saves all normalized paths within their appropriate environments, making it much faster subsequent times within the same script, and independent of working directory.

5. if this.path() does not find an executing script, it throws an error. This is better than whereami::thisfile() which returns NULL when it cannot find the executing script. If the executing script cannot be found, obviously there is a problem that needs to be addressed, so the script should not continue.

Ignoring the direct comparison of this.path and whereami, whereami has some objectively incorrect coding issues and poor recommendations for how you should structure your projects.

1. It treats R and Rscript as two separate applications to look for command line arguments. At least since R 2.5.0 (>= 15 years ago), Rscript directly calls R, so there should not be separate cases. Additionally, it does NOT take into account the differences between the command line applications on Windows and Unix.

2. It checks for uses of knitr::knit() after checking the entire call stack for source() and checking the command line arguments. This is incorrect, it should be checking for knitr::knit() at the same time as it checks for source().

3. When whereami is loaded or attached, it changes option keep.source to TRUE. A package should never be changing global options without asking / / informing the user beforehand. This may not harm your code, but it is still bad practice that should be avoided, especially for a CRAN package.

4. When you call whereami::thisfile(), it forces knitr to be loaded as well. Again, it is changing your environment without permission. It should use something like isNamespaceLoaded("knitr") instead of requireNamespace("knitr") because, contrary to what the package claims, whereami should enhance rather than require knitr.

5. Code aside, whereami suggests that an R script needing to know its own path should only be done if absolutely necessary, and that it should be set outside the context of the R script if possible. I find this answer vague and unconvincing. Other scripting languages have methods of requesting a script's path without issue, so R should too. We shouldn't be scaring programmers into thinking that this is rule-breaking or bad practice.

this.path vs here

If you're not using this.path for the function this.path(), you're probably using it for this.path::here(). The only equivalent (that I know of) is R package here with its function here::here(). this.path provides a mechanism for specifying a path relative to the executing script's directory, while here provides a mechanism for specifying a path relative to the project's directory.

As a long time here user, I appreciate all the functionality and convenience this package offered, but it has some faults that I could not ignore (which this.path fixes). I do not dislike here, I just no longer fit my use-case.

1. here does not work when two projects rely on each other. In my scenario, I had project A and B, both of which rarely relied on the other (so I did not want to combine them into one project), but had once instance in which they ran a script from the other project. However, the project root was already set to the root of project A, so when I tried to run the script in project B from a script in project A, the project root did not update and the script in project B would fail.

2. here does not work when a project is stored on the internet. When I say on the internet, I am not referring to a project stored on a network share, that works correctly. I'm talking about projects uploaded to a website. The work I do requires that all source code and input be publicly available through our website, and that the code should run as expected (slow as it may be, and only code that exclusively reads files and / / or produces graphics). Since the project root of here cannot be a URL, I can't use it.

It should be noted that if you prefer specifying files relative to the project's directory instead of the executing script's directory, you could use this.path::this.proj() instead. It behaves very similarly to here::here(), but can handle multiple projects in use at once, and can run projects stored on the internet.

Other methods

There are a few alternatives to this.path(), though they are very limiting.

Change working directory

You could always change the working directory to the directory of the executing R script before running it. This would be

cd /path/to
Rscript file.R

or

source("/path/to/file.R", chdir = TRUE)

This works for a lot of use-cases, except for interactive use where you probably aren't changing the working directory as you move from file to file, and it won't if your R script is stored on a website. Sometimes it is convenient to have the working directory set elsewhere. This also means that you cannot make R scripts that act like executables.

For example, the Rscript executable needs to know its own path so that it can invoke the R executable. It would be bad practice for Rscript to change the working directory before invoking R, the working directory is your directory, not Rscript's directory. Similarly, if you made an R script that acts like an executable, calling other scripts in the same directory, you could not call those other scripts without the original script knowing its path.

utils::getSrcFilename()

You could use utils::getSrcFilename(). Everywhere you would use this.path(), use utils::getSrcFilename(function() NULL, full.names = TRUE) instead (yes, it is quite lengthy), and everywhere you would use this.dir(), use utils::getSrcDirectory(function() NULL) (again, quite lengthy).

While this will work for R scripts uploaded to a website, this will not work in interactive use since you have to source your scripts. Also, it means you must have option 'keep.source' set to TRUE, once again, probably not a big deal, but something that may cause issues. This means you couldn't run your R scripts from a shell ever again, making it an incredibly inconvenient substitute.

Closing

If you think I've overlooked something in whereami or here, or think there are any improvements I could make to this.path, please let me know, I'm open to all suggestions! And I hope this package serves you well!