[Rd] invert argument in grep

From: Romain Francois <rfrancois_at_mango-solutions.com>
Date: Thu 09 Nov 2006 - 10:14:27 GMT


Hello,

What about an `invert` argument in grep, to return elements that are *not* matching a regular expression :

R> grep("pink", colors(), invert = TRUE, value = TRUE)

would essentially return the same as :

R> colors() [ - grep("pink", colors()) ]

I'm attaching the files that I modified (against today's tarball) for that purpose.

Cheers,

Romain

-- 
*mangosolutions*
/data analysis that delivers/

Tel   +44 1249 467 467
Fax   +44 1249 467 468


grep <- function(pattern, x, ignore.case = FALSE, extended = TRUE, perl = FALSE, value = FALSE, fixed = FALSE, useBytes = FALSE, invert = FALSE) { pattern <- as.character(pattern) ## when value = TRUE we return names if(!is.character(x)) x <- structure(as.character(x), names=names(x)) ## behaves like == for NA pattern if (is.na(pattern)) { if(value) return(structure(rep.int(as.character(NA), length(x)), names = names(x))) else return(rep.int(NA, length(x))) } if(perl) .Internal(grep.perl(pattern, x, ignore.case, value, useBytes, invert)) else .Internal(grep(pattern, x, ignore.case, extended, value, fixed, useBytes, invert))
}
sub <- function(pattern, replacement, x, ignore.case = FALSE, extended = TRUE, perl = FALSE, fixed = FALSE, useBytes = FALSE) { pattern <- as.character(pattern) replacement <- as.character(replacement) if(!is.character(x)) x <- as.character(x) if (is.na(pattern)) return(rep.int(as.character(NA), length(x))) if(perl) .Internal(sub.perl(pattern, replacement, x, ignore.case, useBytes)) else .Internal(sub(pattern, replacement, x, ignore.case, extended, fixed, useBytes))
}
gsub <- function(pattern, replacement, x, ignore.case = FALSE, extended = TRUE, perl = FALSE, fixed = FALSE, useBytes = FALSE) { pattern <- as.character(pattern) replacement <- as.character(replacement) if(!is.character(x)) x <- as.character(x) if (is.na(pattern)) return(rep.int(as.character(NA), length(x))) if(perl) .Internal(gsub.perl(pattern, replacement, x, ignore.case, useBytes)) else .Internal(gsub(pattern, replacement, x, ignore.case, extended, fixed, useBytes))
}
regexpr <- function(pattern, text, extended = TRUE, perl = FALSE, fixed = FALSE, useBytes = FALSE) { pattern <- as.character(pattern) text <- as.character(text) if(perl) .Internal(regexpr.perl(pattern, text, useBytes)) else .Internal(regexpr(pattern, text, extended, fixed, useBytes))
}
gregexpr <- function(pattern, text, extended = TRUE, perl = FALSE, fixed = FALSE, useBytes = FALSE) { pattern <- as.character(pattern) text <- as.character(text) if(perl) .Internal(gregexpr.perl(pattern, text, useBytes)) else .Internal(gregexpr(pattern, text, extended, fixed, useBytes))
}
agrep <- function(pattern, x, ignore.case = FALSE, value = FALSE, max.distance = 0.1) { pattern <- as.character(pattern) if(!is.character(x)) x <- as.character(x) ## behaves like == for NA pattern if (is.na(pattern)){ if (value) return(structure(rep.int(as.character(NA), length(x)), names = names(x))) else return(rep.int(NA, length(x))) } if(!is.character(pattern) || (length(pattern) < 1) || ((n <- nchar(pattern)) == 0)) stop("'pattern' must be a non-empty character string") if(!is.list(max.distance)) { if(!is.numeric(max.distance) || (max.distance < 0)) stop("'max.distance' must be non-negative") if(max.distance < 1) # transform percentages max.distance <- ceiling(n * max.distance) max.insertions <- max.deletions <- max.substitutions <- max.distance } else { ## partial matching table <- c("all", "deletions", "insertions", "substitutions") ind <- pmatch(names(max.distance), table) if(any(is.na(ind))) warning("unknown match distance components ignored") max.distance <- max.distance[!is.na(ind)] names(max.distance) <- table[ind] ## sanity checks comps <- unlist(max.distance) if(!all(is.numeric(comps)) || any(comps < 0)) stop("'max.distance' components must be non-negative") ## extract restrictions if(is.null(max.distance$all)) max.distance$all <- 0.1 max.insertions <- max.deletions <- max.substitutions <- max.distance$all if(!is.null(max.distance$deletions)) max.deletions <- max.distance$deletions if(!is.null(max.distance$insertions)) max.insertions <- max.distance$insertions if(!is.null(max.distance$substitutions)) max.substitutions <- max.distance$substitutions max.distance <- max.distance$all ## transform percentages if(max.distance < 1) max.distance <- ceiling(n * max.distance) if(max.deletions < 1) max.deletions <- ceiling(n * max.deletions) if(max.insertions < 1) max.insertions <- ceiling(n * max.insertions) if(max.substitutions < 1) max.substitutions <- ceiling(n * max.substitutions) } .Internal(agrep(pattern, x, ignore.case, value, max.distance, max.deletions, max.insertions, max.substitutions))
}

\name{grep} \title{Pattern Matching and Replacement} \alias{grep} \alias{sub} \alias{gsub} \alias{regexpr} \alias{gregexpr} \description{ \code{grep} searches for matches to \code{pattern} (its first argument) within the character vector \code{x} (second argument). \code{regexpr} and \code{gregexpr} do too, but return more detail in a different format. \code{sub} and \code{gsub} perform replacement of matches determined by regular expression matching.
}
\usage{ grep(pattern, x, ignore.case = FALSE, extended = TRUE, perl = FALSE, value = FALSE, fixed = FALSE, useBytes = FALSE, invert = FALSE) sub(pattern, replacement, x, ignore.case = FALSE, extended = TRUE, perl = FALSE, fixed = FALSE, useBytes = FALSE) gsub(pattern, replacement, x, ignore.case = FALSE, extended = TRUE, perl = FALSE, fixed = FALSE, useBytes = FALSE) regexpr(pattern, text, extended = TRUE, perl = FALSE, fixed = FALSE, useBytes = FALSE) gregexpr(pattern, text, extended = TRUE, perl = FALSE, fixed = FALSE, useBytes = FALSE)
}
\arguments{ \item{pattern}{character string containing a \link{regular expression} (or character string for \code{fixed = TRUE}) to be matched in the given character vector. Coerced by \code{\link{as.character}} to a character string if possible.} \item{x, text}{a character vector where matches are sought, or an object which can be coerced by \code{as.character} to a character vector.} \item{ignore.case}{if \code{FALSE}, the pattern matching is \emph{case sensitive} and if \code{TRUE}, case is ignored during matching.} \item{extended}{if \code{TRUE}, extended regular expression matching is used, and if \code{FALSE} basic regular expressions are used.} \item{perl}{logical. Should perl-compatible regexps be used? Has priority over \code{extended}.} \item{value}{if \code{FALSE}, a vector containing the (\code{integer}) indices of the matches determined by \code{grep} is returned, and if \code{TRUE}, a vector containing the matching elements themselves is returned.} \item{fixed}{logical. If \code{TRUE}, \code{pattern} is a string to be matched as is. Overrides all conflicting arguments.} \item{useBytes}{logical. If \code{TRUE} the matching is done byte-by-byte rather than character-by-character. See Details.} \item{replacement}{a replacement for matched pattern in \code{sub} and \code{gsub}. Coerced to character if possible. For \code{fixed = FALSE} this can include backreferences \code{"\\1"} to \code{"\\9"} to parenthesized subexpressions of \code{pattern}. For \code{perl = TRUE} only, it can also contain \code{"\\U"} or \code{"\\L"} to convert the rest of the replacement to upper or lower case. } \item{invert}{logical. If \code{TRUE}, then the match is reversed in order to get the items (or the values) that are \emph{not} matching the pattern}
}
\details{ Arguments which should be character strings or character vectors are coerced to character if possible. The two \code{*sub} functions differ only in that \code{sub} replaces only the first occurrence of a \code{pattern} whereas \code{gsub} replaces all occurrences. For \code{regexpr} it is an error for \code{pattern} to be \code{NA}, otherwise \code{NA} is permitted and matches only itself. The regular expressions used are those specified by POSIX 1003.2, either extended or basic, depending on the value of the \code{extended} argument, unless \code{perl = TRUE} when they are those of PCRE, \url{
http://www.pcre.org/}. (The exact set of patterns supported may depend on the version of PCRE installed on the system in use, if \R was configured to use the system PCRE. \R's internal copy used PCRE 6.7.) \code{useBytes} is only used if \code{fixed = TRUE} or \code{perl = TRUE}. For \code{grep} its main effect is to avoid errors/warnings about invalid inputs, but for \code{regexpr} it changes the interpretation of the output.
}
\value{ For \code{grep} a vector giving either the indices of the elements of \code{x} that yielded a match or, if \code{value} is \code{TRUE}, the matched elements of \code{x} (after coercion, preserving names but no other attributes). For \code{sub} and \code{gsub} a character vector of the same length and with the same attributes as \code{x} (after possible coercion). For \code{regexpr} an integer vector of the same length as \code{text} giving the starting position of the first match, or \eqn{-1} if there is none, with attribute \code{"match.length"} giving the length of the matched text (or \eqn{-1} for no match). In a multi-byte locale these quantities are in characters rather than bytes unless \code{useBytes = TRUE} is used with \code{fixed = TRUE} or \code{perl = TRUE}. For \code{gregexpr} a list of the same length as \code{text} each element of which is an integer vector as in \code{regexpr}, except that the starting positions of every match are given. If in a multi-byte locale the pattern or replacement is not a valid sequence of bytes, an error is thrown. An invalid string in \code{x} or \code{text} is a non-match with a warning for \code{grep} or \code{regexpr}, but an error for \code{sub} or \code{gsub}.
}
\section{Warning}{ The standard regular-expression code has been reported to be very slow when applied to extremely long character strings (tens of thousands of characters or more): the code used when \code{perl = TRUE} seems much faster and more reliable for such usages. The standard version of \code{gsub} does not substitute correctly repeated word-boundaries (e.g. \code{pattern = "\\b"}). Use \code{perl = TRUE} for such matches. The \code{perl = TRUE} option is only implemented for single-byte and UTF-8 encodings, and will warn if used in a non-UTF-8 multi-byte locale (unless \code{useBytes = TRUE}).
}
\references{ Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) \emph{The New S Language}. Wadsworth \& Brooks/Cole (\code{grep})
}
\seealso{ \link{regular expression} (aka \code{\link{regexp}}) for the details % the `aka' above is for ESS (and ?reg....) where a space is problematic of the pattern specification. \code{\link{glob2rx}} to turn wildcard matches into regular expressions. \code{\link{agrep}} for approximate matching. \code{\link{tolower}}, \code{\link{toupper}} and \code{\link{chartr}} for character translations. \code{\link{charmatch}}, \code{\link{pmatch}}, \code{\link{match}}. \code{\link{apropos}} uses regexps and has nice examples.
}
\examples{ grep("[a-z]", letters) txt <- c("arm","foot","lefroo", "bafoobar") if(any(i <- grep("foo",txt))) cat("'foo' appears at least once in\n\t",txt,"\n") i # 2 and 4 txt[i] ## Double all 'a' or 'b's; "\\" must be escaped, i.e., 'doubled' %% and escaped even once more in this *.Rd file! gsub("([ab])", "\\\\1_\\\\1_", "abc and ABC") txt <- c("The", "licenses", "for", "most", "software", "are", "designed", "to", "take", "away", "your", "freedom", "to", "share", "and", "change", "it.", "", "By", "contrast,", "the", "GNU", "General", "Public", "License", "is", "intended", "to", "guarantee", "your", "freedom", "to", "share", "and", "change", "free", "software", "--", "to", "make", "sure", "the", "software", "is", "free", "for", "all", "its", "users") ( i <- grep("[gu]", txt) ) # indices stopifnot( txt[i] == grep("[gu]", txt, value = TRUE) ) ## Note that in locales such as en_US this includes B as the ## collation order is aAbBcCdEe ... (ot <- sub("[b-e]",".", txt)) txt[ot != gsub("[b-e]",".", txt)]#- gsub does "global" substitution txt[gsub("g","#", txt) != gsub("g","#", txt, ignore.case = TRUE)] # the "G" words regexpr("en", txt) gregexpr("e", txt) ## trim trailing white space str = 'Now is the time ' sub(' +$', '', str) ## spaces only sub('[[:space:]]+$', '', str) ## white space, POSIX-style sub('\\\\s+$', '', str, perl = TRUE) ## Perl-style white space ## capitalizing gsub("(\\\\w)(\\\\w*)", "\\\\U\\\\1\\\\L\\\\2", "a test of capitalizing", perl=TRUE) gsub("\\\\b(\\\\w)", "\\\\U\\\\1", "a test of capitalizing", perl=TRUE)
}
\keyword{character} \keyword{utilities}

______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel

Received on Fri Nov 10 17:59:26 2006

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.1.8, at Fri 10 Nov 2006 - 15:30:41 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-devel. Please read the posting guide before posting to the list.