The rprojroot package solves a seemingly trivial but annoying problem that occurs sooner or later in any largish project: How to find files in subdirectories? Ideally, file paths are relative to the project root.

Unfortunately, we cannot always be sure about the current working directory: For instance, in RStudio it’s sometimes:

  • the project root (when running R scripts),
  • a subdirectory (when building vignettes),
  • again the project root (when executing chunks of a vignette).
basename(getwd())
## [1] "articles"

In some cases, it’s even outside the project root.

This vignette starts with a very brief summary that helps you get started, followed by a longer description of the features.

TL;DR

What is your project: An R package?

rprojroot::is_r_package
## Root criterion: Contains a file 'DESCRIPTION' with contents matching '^Package: '

Or an RStudio project?

rprojroot::is_rstudio_project
## Root criterion: Contains a file matching '[.]Rproj$' with contents matching '^Version: ' in the first 1 lines

Or something else?

rprojroot::has_file(".git/index")
## Root criterion: Contains a file '.git/index'

For now, we assume it’s an R package:

root <- rprojroot::is_r_package

The root object contains a function that helps locating files below the root of your package, regardless of your current working directory. If you are sure that your working directory is somewhere below your project’s root, use the root$find_file() function:

readLines(root$find_file("DESCRIPTION"), 3)
## [1] "Package: rprojroot"                            
## [2] "Title: Finding Files in Project Subdirectories"
## [3] "Version: 1.1"

You can also construct an accessor to your root using the root$make_fix_file() function:

root_file <- root$make_fix_file()

Note that root_file() is a function that works just like $find_file() but will find the files even if the current working directory is outside your project:

withr::with_dir(
  "../..",
  readLines(root_file("DESCRIPTION"), 3)
)
## [1] "Package: rprojroot"                            
## [2] "Title: Finding Files in Project Subdirectories"
## [3] "Version: 1.1"

If you know the absolute path of some directory below your project, but cannot be sure of your current working directory, pass that absolute path to root$make_fix_file():

root_file <- root$make_fix_file("C:\\Users\\User Name\\...")

Get the path of standalone R scripts or vignettes using the thisfile() function in the kimisc package:

root_file <- root$make_fix_file(dirname(kimisc::thisfile()))

The remainder of this vignette describes implementation details and advanced features.

Project root

We assume a self-contained project where all files and directories are located below a common root directory. Also, there should be a way to unambiguously identify this root directory. (Often, the root contains a regular file whose name matches a given pattern, and/or whose contents match another pattern.) In this case, the following method reliably finds our project root:

  • Start the search in any subdirectory of our project
  • Proceed up the directory hierarchy until the root directory has been identified

The Git version control system (and probably many other tools) use a similar approach: A Git command can be executed from within any subdirectory of a repository.

A simple example

The find_root() function implements the core functionality. It returns the path to the first directory that matches the filtering criteria, or throws an error if there is no such directory. Filtering criteria are constructed in a generic fashion using the root_criterion() function, the has_file() function constructs a criterion that checks for the presence of a file with a specific name and specific contents.

library(rprojroot)

# List all files and directories below the root
dir(find_root(has_file("DESCRIPTION")))
##  [1] "_pkgdown.yml"     "appveyor.yml"     "cran-comments.md"
##  [4] "DESCRIPTION"      "docs"             "inst"            
##  [7] "Makefile"         "man"              "NAMESPACE"       
## [10] "NEWS.md"          "R"                "readme"          
## [13] "README.md"        "revdep"           "rprojroot.Rproj" 
## [16] "tests"            "tic.R"            "vignettes"
# Find a file relative to the root
file.exists(find_root_file("R", "root.R", criterion = has_file("DESCRIPTION")))
## [1] TRUE

Note that the following code produces identical results when building the vignette and when sourcing the chunk in RStudio, provided that the current working directory is the project root or anywhere below.

Criteria

The has_file() function (and the more general root_criterion()) both return an S3 object of class root_criterion:

has_file("DESCRIPTION")
## Root criterion: Contains a file 'DESCRIPTION'

In addition, character values are coerced to has_file criteria by default, this coercion is applied automatically by find_root(). (This feature is used by the introductory example.)

as.root_criterion("DESCRIPTION")
## Root criterion: Contains a file 'DESCRIPTION'

The return value of these functions can be stored and reused; in fact, the package provides 5 such criteria:

criteria
## $is_rstudio_project
## Root criterion: Contains a file matching '[.]Rproj$' with contents matching '^Version: ' in the first 1 lines
## 
## $is_r_package
## Root criterion: Contains a file 'DESCRIPTION' with contents matching '^Package: '
## 
## $is_remake_project
## Root criterion: Contains a file 'remake.yml'
## 
## $is_testthat
## Root criterion: Directory name is 'testthat' (also look in subdirectories: 'tests/testthat', 'testthat')
## 
## $from_wd
## Root criterion: From current working directory
## 
## attr(,"class")
## [1] "root_criteria"

Defining new criteria is easy:

has_license <- has_file("LICENSE")
has_license
## Root criterion: Contains a file 'LICENSE'
is_projecttemplate_project <- has_file("config/global.dcf", "^version: ")
is_projecttemplate_project
## Root criterion: Contains a file 'config/global.dcf' with contents matching '^version: '

You can also combine criteria via the | operator:

is_r_package | is_rstudio_project
## Root criterion: Contains a file 'DESCRIPTION' with contents matching '^Package: ', or Contains a file matching '[.]Rproj$' with contents matching '^Version: ' in the first 1 lines

Shortcuts

To avoid specifying the search criteria for the project root every time, shortcut functions can be created. The find_package_root_file() is a shortcut for find_root_file(..., criterion = is_r_package):

# Print first lines of the source for this document
head(readLines(find_package_root_file("vignettes", "rprojroot.Rmd")))
## [1] "---"                                               
## [2] "title: \"Finding files in project subdirectories\""
## [3] "author: \"Kirill Müller\""                         
## [4] "date: \"`r Sys.Date()`\""                          
## [5] "output: rmarkdown::html_vignette"                  
## [6] "vignette: >"

To save typing effort, define a shorter alias:

P <- find_package_root_file

# Use a shorter alias
file.exists(P("vignettes", "rprojroot.Rmd"))
## [1] TRUE

Each criterion actually contains a function that allows finding a file below the root specified by this criterion. As our project does not have a file named LICENSE, querying the root results in an error:

# Use the has_license criterion to find the root
R <- has_license$find_file
R
## function (..., path = ".") 
## {
##     find_root_file(..., criterion = criterion, path = path)
## }
## <environment: 0x42412a0>
# Our package does not have a LICENSE file, trying to find the root results in an error
R()
## Error: No root directory found. Test criterion:
## Contains a file 'LICENSE'

Fixed root

We can also create a function that computes a path relative to the root at creation time.

# Define a function that computes file paths below the current root
F <- is_r_package$make_fix_file()
F
## function (...) 
## {
##     file.path("/home/travis/build/krlmlr/rprojroot", ...)
## }
## <environment: 0x59484e0>
# Show contents of the NAMESPACE file in our project
readLines(F("NAMESPACE"))
##  [1] "# Generated by roxygen2: do not edit by hand"
##  [2] ""                                            
##  [3] "S3method(\"|\",root_criterion)"              
##  [4] "S3method(as.root_criterion,character)"       
##  [5] "S3method(as.root_criterion,default)"         
##  [6] "S3method(as.root_criterion,root_criterion)"  
##  [7] "S3method(format,root_criterion)"             
##  [8] "S3method(print,root_criterion)"              
##  [9] "S3method(str,root_criteria)"                 
## [10] "export(as.root_criterion)"                   
## [11] "export(criteria)"                            
## [12] "export(find_package_root_file)"              
## [13] "export(find_remake_root_file)"               
## [14] "export(find_root)"                           
## [15] "export(find_root_file)"                      
## [16] "export(find_rstudio_root_file)"              
## [17] "export(find_testthat_root_file)"             
## [18] "export(from_wd)"                             
## [19] "export(has_dirname)"                         
## [20] "export(has_file)"                            
## [21] "export(has_file_pattern)"                    
## [22] "export(is.root_criterion)"                   
## [23] "export(is_r_package)"                        
## [24] "export(is_remake_project)"                   
## [25] "export(is_rstudio_project)"                  
## [26] "export(is_testthat)"                         
## [27] "export(root_criterion)"                      
## [28] "import(backports)"                           
## [29] "importFrom(utils,str)"

This is a more robust alternative to $find_file(), because it fixes the project directory when $make_fix_file() is called, instead of searching for it every time. (For that reason it is also slightly faster, but I doubt this matters in practice.)

This function can be used even if we later change the working directory to somewhere outside the project:

# Print the size of the namespace file, working directory outside the project
withr::with_dir(
  "../..",
  file.size(F("NAMESPACE"))
)
## [1] 752

The make_fix_file() member function also accepts an optional path argument, in case you know your project’s root but the current working directory is somewhere outside. Take a look at the thisfile() function in the kimisc package for getting the path to the current script or knitr document.

testthat files

Tests run with testthat commonly use files that live below the tests/testthat directory. Ideally, this should work in the following situation:

  • During package development (working directory: package root)
  • When testing with devtools::test() (working directory: tests/testthat)
  • When running R CMD check (working directory: a renamed recursive copy of tests)

The is_testthat criterion allows robust lookup of test files.

is_testthat
## Root criterion: Directory name is 'testthat' (also look in subdirectories: 'tests/testthat', 'testthat')

The example code below lists all files in the hierarchy test directory. It uses two project root lookups in total, so that it also works when rendering the vignette (sigh):

dir(is_testthat$find_file("hierarchy", path = is_r_package$find_file()))
## [1] "a"               "b"               "c"               "DESCRIPTION"    
## [5] "hierarchy.Rproj"

Summary

The rprojroot package allows easy access to files below a project root if the project root can be identified easily, e.g. if it is the only directory in the whole hierarchy that contains a specific file. This is a robust solution for finding files in largish projects with a subdirectory hierarchy if the current working directory cannot be assumed fixed. (However, at least initially, the current working directory must be somewhere below the project root.)

Acknowledgement

This package was inspired by the gist “Stop the working directory insanity” by Jennifer Bryan, and by the way Git knows where its files are.