Pattern Matching

Strongly typed wrappers around grep that have the value (see note), ignore.case and fixed arguments set internally (as well as the conflicting arguments).

If grepv is found in the current R version, it is reexported from base.

Usage

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

grepvf(pattern, x, useBytes = FALSE, invert = FALSE)

grepvi(pattern, x, perl = FALSE, useBytes = FALSE, invert = FALSE)

Arguments

pattern: character string containing a regular expression (or character string for fixed = TRUE to be matched in the given character vector. Coerced by as.character to a character string if possible. If a character vector of length 2 or more is supplied, the first element is used with a warning. Missing values are allowed.
x: a character vector where matches are sought, or an object which can be coerced by as.character to a character vector. Long vectors are supported.
ignore.case: logical. if FALSE, the pattern matching is case sensitive and if TRUE, case is ignored during matching.
perl: logical. Should Perl-compatible regexps be used?
value: logical. If FALSE, a vector containing the (integer) indices of the matches determined by grep is returned, and if TRUE, a vector containing the matching elements themselves is returned.
fixed: logical. If TRUE, pattern is a string to be matched as is. Overrides all conflicting arguments.
useBytes: logical. If TRUE the matching is done byte-by-byte rather than character-by-character.
invert: logical. If TRUE return indices or values for elements that do not match.

Value

character vector containing the selected elements of x (after coercion, preserving names but no other attributes).

grepv() can also return a vector of the indices of the elements of x that yielded a match (or not, for invert = TRUE) if value = FALSE (see note). This will be an integer vector unless the input is a long vector, when it will be a double vector.

Details

*f() suffixed functions have fixed = TRUE and conflicting arguments (perl and ignore.case) set as FALSE.

*i() suffixed functions have ignore.case = TRUE and the conflicting fixed argument set as FALSE.

For full documentation of the wrapped functions, see the help pages for grep.

Note

suppr wrappers of the base grep/sub functions remove the arguments that relate to the strong typing, just like grepl does by not having a value argument. However, the base grepv implementation has kept the value argument, so the version here keeps the value argument for compatibility.

Examples

grepv("foo", c("foo", "Foo", "bar"))
#> [1] "foo"
grepvf("foo", c("foo", "Foo", "bar"))
#> [1] "foo"
grepvi("foo", c("foo", "Foo", "bar"))
#> [1] "foo" "Foo"