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Require usage of direct methods for subsetting strings via regex

Source: R/regex_subset_linter.R
regex_subset_linter.Rd

Using 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).

Usage

regex_subset_linter()

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.

Tags

best_practices, efficiency, regex

Examples

# will produce lints
lint(
  text = "x[grep(pattern, x)]",
  linters = regex_subset_linter()
)
#> <text>:1:3: warning: [regex_subset_linter] Prefer grep(pattern, x, ..., value = TRUE) over x[grep(pattern, x, ...)] and x[grepl(pattern, x, ...)].
#> x[grep(pattern, x)]
#>   ^~~~~~~~~~~~~~~~

lint(
  text = "x[stringr::str_which(x, pattern)]",
  linters = regex_subset_linter()
)
#> <text>:1:3: warning: [regex_subset_linter] Prefer stringr::str_subset(x, pattern) over x[str_detect(x, pattern)] and x[str_which(x, pattern)].
#> x[stringr::str_which(x, pattern)]
#>   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# okay
lint(
  text = "grep(pattern, x, value = TRUE)",
  linters = regex_subset_linter()
)
#> ℹ No lints found.

lint(
  text = "stringr::str_subset(x, pattern)",
  linters = regex_subset_linter()
)
#> ℹ No lints found.