Pattern Matching

Strongly typed wrappers around grep that have the fixed and ignore.case arguments set internally.

Usage

grepf(pattern, x, value = FALSE, useBytes = FALSE, invert = FALSE)

grepi(
  pattern,
  x,
  perl = FALSE,
  value = 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.

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.

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.

perl

logical. Should Perl-compatible regexps be used?

Value

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

with value = TRUE, return a character vector containing the selected elements of x (after coercion, preserving names but no other attributes).

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.

See also

Other pattern-match-replacement-wrappers: grepl-wrappers, grepv-wrappers, sub-wrappers

Examples

grepf("foo", c("foo", "Foo", "bar"))
#> [1] 1
grepf("foo", c("foo", "Foo", "bar"), value = TRUE)
#> [1] "foo"
grepi("foo", c("foo", "Foo", "bar"))
#> [1] 1 2
grepi("foo", c("foo", "Foo", "bar"), value = TRUE)
#> [1] "foo" "Foo"