grep {base}

R Documentation

Pattern Matching and Replacement

Description

grep searches for matches to pattern given as its first argument within the the vector of character strings given as its second argument.

sub and gsub perform replacement of matches determined by regular expression matching. The functions differ only in that sub replaces only the first occurence of a pattern whereas gsub replaces all occurences.

The regular expressions used are those specified by POSIX 1003.2, either extended or basic, depending on the value of the extended argument.

Usage

grep(pattern, x, ignore.case=FALSE, extended=TRUE, value=FALSE)
sub(pattern, replacement, x,
        ignore.case=FALSE, extended=TRUE)
gsub(pattern, replacement, x,
        ignore.case=FALSE, extended=TRUE)

Arguments

pattern	character string containing a regular expression to be matched in the vector of character string vec.
x	a vector of character strings where matches is sought.
ignore.case	if FALSE, the pattern matching is case sensitive and if TRUE, case is ignored during matching.
extended	if TRUE, extended regular expression matching is used, and if FALSE basic regular expressions are used.
value	if FALSE, a vector containing the indices of the matches determined by grep is returned, and if TRUE, a vector containing the matching elements themselves is returned.
replacement	a replacement for matched pattern in sub and gsub.

Note

This function is based on the regex regular expression library written by Henry Spencer of the University of Toronto.

See Also

match, pmatch.

Examples

grep("[a-z]", letters)

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