Pattern Matching for Raw Vectors - R Documentation

`grepRaw` Pattern Matching for Raw Vectors

Description

grepRaw searches for substring pattern matches within a raw vector x.

Usage

grepRaw(pattern, x, offset = 1L, ignore.case = FALSE,
        value = FALSE, fixed = FALSE, all = FALSE, invert = FALSE)

Arguments

`pattern`	raw vector containing a regular expression (or fixed pattern for `fixed = TRUE`) to be matched in the given raw vector. Coerced by `charToRaw` to a character string if possible.
`x`	a raw vector where matches are sought, or an object which can be coerced by `charToRaw` to a raw vector. Long vectors are not supported.
`ignore.case`	if `FALSE`, the pattern matching is case sensitive and if `TRUE`, case is ignored during matching.
`offset`	An integer specifying the offset from which the search should start. Must be positive. The beginning of line is defined to be at that offset so `"^"` will match there.
`value`	logical. Determines the return value: see ‘Value’.
`fixed`	logical. If `TRUE`, `pattern` is a pattern to be matched as is.
`all`	logical. If `TRUE` all matches are returned, otherwise just the first one.
`invert`	logical. If `TRUE` return indices or values for elements that do not match. Ignored (with a warning) unless `value = TRUE`.

Details

Unlike grep, seeks matching patterns within the raw vector x . This has implications especially in the all = TRUE case, e.g., patterns matching empty strings are inherently infinite and thus may lead to unexpected results.

The argument invert is interpreted as asking to return the complement of the match, which is only meaningful for value = TRUE. Argument offset determines the start of the search, not of the complement. Note that invert = TRUE with all = TRUE will split x into pieces delimited by the pattern including leading and trailing empty strings (consequently the use of regular expressions with "^" or "$" in that case may lead to less intuitive results).

Some combinations of arguments such as fixed = TRUE with value = TRUE are supported but are less meaningful.

Value

grepRaw(value = FALSE) returns an integer vector of the offsets at which matches have occurred. If all = FALSE then it will be either of length zero (no match) or length one (first matching position).

grepRaw(value = TRUE, all = FALSE) returns a raw vector which is either empty (no match) or the matched part of x.

grepRaw(value = TRUE, all = TRUE) returns a (potentially empty) list of raw vectors corresponding to the matched parts.

Source

The TRE library of Ville Laurikari (https://github.com/laurikari/tre/) is used except for fixed = TRUE.

Examples

grepRaw("no match", "textText")  # integer(0): no match
grepRaw("adf", "adadfadfdfadadf") # 3 - the first match
grepRaw("adf", "adadfadfdfadadf", all=TRUE, fixed=TRUE)
## [1]  3  6 13 -- three matches

grepRaw Pattern Matching for Raw Vectors