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Detect and count matches

Source: R/detect.R
re_detect.Rd

re_detect() reports whether each element of x matches its pattern. re_count() counts the non-overlapping matches in each element.

Usage

re_detect(
  x,
  pattern,
  anchor = c("none", "start", "full"),
  negate = FALSE,
  flags = "",
  literal = FALSE,
  limits = NULL
)

re_count(x, pattern, flags = "", literal = FALSE, limits = NULL)

Arguments

x

A character vector, a raw vector, or a list of raw vectors. NA (or NULL in a list) gives NA.

pattern

A character vector or an re vector; see Patterns.

anchor

Where a match must be: "none" anywhere, "start" at the start of the subject (Python's re.match()), "full" the whole subject (Python's re.fullmatch()). Anchoring is done by PCRE2, so it holds for every branch of a top-level alternation.

negate

If TRUE, return TRUE for elements that do not match.

flags

A single string of flag letters for pattern strings, such as "i" for case-insensitive matching; see re_compile() for every letter. It applies to every pattern in the call.

literal

If TRUE, each pattern string is matched as literal text, with no metacharacters, as base R's fixed = TRUE. Only the flags i and r apply to a literal pattern.

limits

A re_limits() object, or NULL for getOption("zuregex.limits") and then PCRE2's defaults.

Value

re_detect(): a logical vector, one per subject. re_count(): an integer vector, one per subject.

Patterns

pattern is a character vector of regular expressions, compiled through the cache with flags and literal, or an re vector from re_compile(), which carries its own flags and can use the JavaScript dialect. It has length 1, used for every element of x, or exactly the length of x, pairing pattern[i] with x[i]. Any other length is an error: nothing is recycled. An NA pattern gives NA for its element.

Base R's options map onto these arguments: ignore.case = TRUE is flags = "i", fixed = TRUE is literal = TRUE, invert = TRUE is re_detect(negate = TRUE), and useBytes = TRUE is a raw vector or strings marked as "bytes" (see Strings and bytes). perl = TRUE is always on.

Strings and bytes

Character input is matched as UTF-8; strings in other declared encodings are translated first. Invalid UTF-8 is an error of class zuregex_error_utf. A raw vector is one subject matched as bytes, as is each element of a list of raw vectors, and so is a character vector with any element marked as "bytes". Patterns are then compiled without UTF-8 support, so . matches one byte. \\C, which matches one byte, is allowed only then: in a UTF-8 pattern it is a compile error, since it could split a character. A bytes pattern may not turn UTF-8 back on with (*UTF).

Examples

x <- c("apple", "banana", "cherry", NA)
re_detect(x, "an")
#> [1] FALSE  TRUE FALSE    NA
re_detect(x, "a|b", anchor = "start")
#> [1]  TRUE  TRUE FALSE    NA
re_count(x, "[aeiou]")
#> [1]  2  3  1 NA
re_detect(x, "APPLE", flags = "i")
#> [1]  TRUE FALSE FALSE    NA
re_count("a.b.c", ".", literal = TRUE)
#> [1] 2

# One pattern per element
re_detect(c("abc", "abc"), c("^a", "^b"))
#> [1]  TRUE FALSE