Extract or replace matched substrings from match data obtained by
a character vector
an object with match data
a logical: if
an object with suitable replacement values for the
matched or non-matched substrings (see
the matched substrings as specified by the match data. For vector
match data (as obtained from
regexpr), empty matches are
dropped; for list match data, empty matches give empty components
(zero-length character vectors).
regmatches extracts the
non-matched substrings, i.e., the strings are split according to the
matches similar to
strsplit (for vector match data, at
most a single split is performed).
regmatches extracts both
non-matched and matched substrings, always starting and ending with a
non-match (empty if the match occurred at the beginning or the end,
Note that the match data can be obtained from regular expression
matching on a modified version of
x with the same numbers of
The replacement function can be used for replacing the matched or
non-matched substrings. For vector match data, if
value should be a character vector with length the
number of matched elements in
m. Otherwise, it should be a
list of character vectors with the same length as
m, each as
long as the number of replacements needed. Replacement coerces values
to character or list and generously recycles values as needed.
Missing replacement values are not allowed.
regmatches, a character vector with the matched substrings
m is a vector and
a list with the matched or/and non-matched substrings.
regmatches<-, the updated character vector.
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x <- c("A and B", "A, B and C", "A, B, C and D", "foobar") pattern <- "[[:space:]]*(,|and)[[:space:]]" ## Match data from regexpr() m <- regexpr(pattern, x) regmatches(x, m) regmatches(x, m, invert = TRUE) ## Match data from gregexpr() m <- gregexpr(pattern, x) regmatches(x, m) regmatches(x, m, invert = TRUE) ## Consider x <- "John (fishing, hunting), Paul (hiking, biking)" ## Suppose we want to split at the comma (plus spaces) between the ## persons, but not at the commas in the parenthesized hobby lists. ## One idea is to "blank out" the parenthesized parts to match the ## parts to be used for splitting, and extract the persons as the ## non-matched parts. ## First, match the parenthesized hobby lists. m <- gregexpr("\\([^)]*\\)", x) ## Write a little utility for creating blank strings with given numbers ## of characters. blanks <- function(n) strrep(" ", n) ## Create a copy of x with the parenthesized parts blanked out. s <- x regmatches(s, m) <- Map(blanks, lapply(regmatches(s, m), nchar)) s ## Compute the positions of the split matches (note that we cannot call ## strsplit() on x with match data from s). m <- gregexpr(", *", s) ## And finally extract the non-matched parts. regmatches(x, m, invert = TRUE)
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