grepl: Detect Pattern Occurrences

In stringx: Replacements for Base String Functions Powered by 'stringi'

Detect Pattern Occurrences

Description

grepl2 indicates whether a string matches the corresponding pattern or not.

grepv2 returns a subset of x matching the corresponding patterns. Its replacement version allows for substituting such a subset with new content.

Usage

grepl2(x, pattern, ..., ignore_case = FALSE, fixed = FALSE, invert = FALSE)

grepv2(x, pattern, ..., ignore_case = FALSE, fixed = FALSE, invert = FALSE)

grepv2(x, pattern, ..., ignore_case = FALSE, fixed = FALSE, invert = FALSE) <- value

grepl(
  pattern,
  x,
  ...,
  ignore.case = FALSE,
  fixed = FALSE,
  invert = FALSE,
  perl = FALSE,
  useBytes = FALSE
)

grep(
  pattern,
  x,
  ...,
  ignore.case = FALSE,
  fixed = FALSE,
  value = FALSE,
  invert = FALSE,
  perl = FALSE,
  useBytes = FALSE
)

Arguments

x	character vector whose elements are to be examined
pattern	character vector of nonempty search patterns; for grepv2 and grep, must not be longer than x
...	further arguments to stri_detect, e.g., max_count, locale, dotall
ignore_case, ignore.case	single logical value; indicates whether matching should be case-insensitive
fixed	single logical value; FALSE for matching with regular expressions (see about_search_regex); TRUE for fixed pattern matching (about_search_fixed); NA for the Unicode collation algorithm (about_search_coll)
invert	single logical value; indicates whether a no-match is rather of interest
value	character vector of replacement strings or a single logical value indicating whether indexes of strings in x matching patterns should be returned
perl, useBytes	not used (with a warning if attempting to do so) [DEPRECATED]

Details

These functions are fully vectorised with respect to x and pattern.

The [DEPRECATED] grepl simply calls grepl2 which have a cleaned-up argument list.

The [DEPRECATED] grep with value=FALSE is actually redundant – it can be trivially reproduced with grepl and which.

grepv2 and grep with value=FALSE combine pattern matching and subsetting and some users may find it convenient in conjunction with the forward pipe operator, |>.

Value

grepl2 and [DEPRECATED] grep return a logical vector. They preserve the attributes of the longest inputs (unless they are dropped due to coercion). Missing values in the inputs are propagated consistently.

grepv2 and [DEPRECATED] grep with value=TRUE returns a subset of x with elements matching the corresponding patterns. [DEPRECATED] grep with value=FALSE returns the indexes in x where a match occurred. Missing values are not included in the outputs and only the names attribute is preserved, because the length of the result may be different than that of x.

The replacement version of grepv2 modifies x 'in-place'.

Differences from Base R

grepl and grep are [DEPRECATED] replacements for base grep and grepl implemented with stri_detect.

• there are inconsistencies between the argument order and naming in grepl, strsplit, and startsWith (amongst others); e.g., where the needle can precede the haystack, the use of the forward pipe operator, |>, is less convenient [fixed by introducing grepl2]

• base R implementation is not portable as it is based on the system PCRE or TRE library (e.g., some Unicode classes may not be available or matching thereof can depend on the current LC_CTYPE category [fixed here]

• not suitable for natural language processing [fixed here – use fixed=NA]

• two different regular expression libraries are used (and historically, ERE was used in place of TRE) [here, ICU Java-like regular expression engine is only available, hence the perl argument has no meaning]

• not vectorised w.r.t. pattern [fixed here, however, in grep, pattern cannot be longer than x]

• missing values in haystack will result in a no-match [fixed in grepl; see Value]

• ignore.case=TRUE cannot be used with fixed=TRUE [fixed here]

• no attributes are preserved [fixed here; see Value]

Author(s)

Marek Gagolewski

See Also

The official online manual of stringx at https://stringx.gagolewski.com/

Related function(s): paste, nchar, strsplit, gsub2, gregexpr2, gregextr2, gsubstr

Examples

x <- c("abc", "1237", "\U0001f602", "\U0001f603", "stringx\U0001f970", NA)
grepl2(x, "\\p{L}")
which(grepl2(x, "\\p{L}"))  # like grep

# at least 1 letter or digit:
p <- c("\\p{L}", "\\p{N}")
`dimnames<-`(outer(x, p, grepl2), list(x, p))

x |> grepv2("\\p{L}")
grepv2(x, "\\p{L}", invert=TRUE) <- "\U0001F496"
print(x)

stringx documentation built on April 3, 2025, 6:17 p.m.