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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).




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().


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.