gappy gappy - 3 months ago 23
R Question

using R to copy files

As part of a larger task performed in R run under windows, I would like to copy selected files between directories. Is it possible to give within R a command like

cp patha/filea*.csv pathb
(notice the wildcard, for extra spice)?

mjv mjv
Answer

I don't think there is a direct way (shy of shelling-out), but something like the following usually works for me.

flist <- list.files("patha", "^filea.+[.]csv$", full.names = TRUE)
file.copy(flist, "pathb")

Notes:

  • I purposely decomposed in two steps, they can be combined.
  • See the regular expression: R uses true regex, and also separates the file pattern from the path, in two separate arguments.
  • note the ^ and $ (beg/end of string) in the regex -- this is a common gotcha, as these are implicit to wildcard-type patterns, but required with regexes (lest some file names which match the wildcard pattern but also start and/or end with additional text be selected as well).
  • In the Windows world, people will typically add the ignore.case = TRUE argument to list.files, in order to emulate the fact that directory searches are case insensitive with this OS.
  • R's glob2rx() function provides a convenient way to convert wildcard patterns to regular expressions. For example fpattern = glob2rx('filea*.csv') returns a different but equivalent regex.