The temporary directory and files
Firstly let’s create a folder to work within a temporary directory. Look for details on how to work with temporary files in R in my post When do you need a temporary directory and files in R and how to use them.
Function tempfile() does not create any files. It generates a random file name, which is unique for the current R session. By default, tempfile() generates a file name in R temporary directory.
mydirname <- tempfile(pattern = "mydir") mydirname [1] "/tmp/RtmpVuBPUY/mydir1e5a69bc39ac"
Exploring file system
In themydirnamevariable, we have a file path where we can create a file. Now there is nothing. Let’s check it with the function file.exists() and the content of the temporary directory with the function dir().
file.exists(mydirname) [1] FALSE dir(tempdir()) character(0) # Empty character vector
Creating a directory
Next, we touch our file system and create the desired directory.
dir.create(mydirname)
And recheck it:
- existence;
- content of the parent directory;
- modification time.
file.exists(mydirname) [1] TRUE dir(tempdir(), full.names = TRUE) [1] "/tmp/RtmpVuBPUY/mydir1e5a69bc39ac" file.mtime(mydirname) [1] "2016-08-17 19:19:37 MSK"
More listings, including R system files
Let’s inspect files from one of the installed R-packages. A command system.file() returns the full path of files from installed packages. We use it to get a file path of stats package.
system.file(package = "stats") [1] "/usr/lib64/R/library/stats"
Next, we list the content of this folder.
dir(system.file(package = "stats")) [1] "COPYRIGHTS.modreg" "demo" "DESCRIPTION" [4] "help" "html" "INDEX" [7] "libs" "Meta" "NAMESPACE" [10] "R" "SOURCES.ts"
We can check the content of any subdirectory. For example, the “demo” folder.
dir(system.file("demo", package = "stats"))
[1] "glm.vr.R" "lm.glm.R" "nlm.R" "smooth.R"
In some situations, you would prefer full names:
dir(system.file("demo", package = "stats"), full.names = TRUE)
[1] "/usr/lib64/R/library/stats/demo/glm.vr.R"
[2] "/usr/lib64/R/library/stats/demo/lm.glm.R"
[3] "/usr/lib64/R/library/stats/demo/nlm.R"
[4] "/usr/lib64/R/library/stats/demo/smooth.R"
Constructing of file names in R
What is a file name? It is a character string. Wrong. It is a system-specific character string.
R function file.path() creates system-specific file names.
workingdir <- "projects" projectdir <- "warandpeace" datadir <- "data" file.path(workingdir, projectdir, datadir) # Linux-based OS [1] "projects/warandpeace/data" # Surprisingly in Windows we have similar results [1] "projects/warandpeace/data"
Note about Windows
Why did file.path() put slashes as separators when we used to backslash in Windows (for example C:\Program Files\R\R-3.3.1)? There is even a special note on it in file.path’s help page:
The components are by default separated by ‘/’ (not ‘\’) on Windows.
Surprisingly DOS and Windows supported slash as file path separators from the beginning. So in most cases, one can use both variants in Windows.