Require usage of direct methods for subsetting strings via regex.
Source:R/regex_subset_linter.R
regex_subset_linter.RdUsing value = TRUE in grep() returns the subset of the input that matches
the pattern, e.g. grep("[a-m]", letters, value = TRUE) will return the
first 13 elements (a through m).
Details
letters[grep("[a-m]", letters)] and letters[grepl("[a-m]", letters)]
both return the same thing, but more circuitously and more verbosely.
The stringr package also provides an even more readable alternative,
namely str_subset(), which should be preferred to versions using
str_detect() and str_which().
Exceptions
Note that x[grep(pattern, x)] and grep(pattern, x, value = TRUE)
are not completely interchangeable when x is not character
(most commonly, when x is a factor), because the output of the
latter will be a character vector while the former remains a factor.
It still may be preferable to refactor such code, as it may be faster
to match the pattern on levels(x) and use that to subset instead.
See also
linters for a complete list of linters available in lintr.