问题
I have an R script that takes a file as input, and I want a general way to know whether the input is a file that exists, and is not a directory.
In Python you would do it this way: How do I check whether a file exists using Python?, but I was struggling to find anything similar in R.
What I'd like is something like below, assuming that the file.txt actually exists:
input.good = "~/directory/file.txt"
input.bad = "~/directory/"
is.file(input.good) # should return TRUE
is.file(input.bad) #should return FALSE
R has something called file.exists(), but this doesn't distinguish files from directories.
回答1:
There is a dir.exists function in all recent versions of R.
file.exists(f) && !dir.exists(f)
回答2:
The solution is to use file_test()
This gives shell-style file tests, and can distinguish files from folders.
E.g.
input.good = "~/directory/file.txt"
input.bad = "~/directory/"
file_test("-f", input.good) # returns TRUE
file_test("-f", input.bad) #returns FALSE
From the manual:
Usage
file_test(op, x, y) Arguments
op a character string specifying the test to be performed. Unary tests (only x is used) are "-f" (existence and not being a directory), "-d" (existence and directory) and "-x" (executable as a file or searchable as a directory). Binary tests are "-nt" (strictly newer than, using the modification dates) and "-ot" (strictly older than): in both cases the test is false unless both files exist.
x, y character vectors giving file paths.
回答3:
You can also use is_file(path) from the fs package.
来源：https://stackoverflow.com/questions/46147901/r-test-if-a-file-exists-and-is-not-a-directory