List files in R that do NOT match a pattern

Question

R has a function to list files in a directory, which is list.files(). It comes with the optional parameter pattern= to list only files

Answer 1

I belive you will have to do it yourself, as list.files does not support Perl regex (so you couldn't do something like pattern=^(?!new_)).

i.e. list all files then filter them with grep:

grep(list.files(path="data"), pattern='new_', invert=TRUE, value=TRUE)

The grep(...) does the pattern matching; invert=TRUE inverts the match; value=TRUE returns the values of the matches (i.e. the filenames) rather than the indices of the matches.