strsplit {base}

R Documentation

Split the Elements of a Character Vector

Description

Split the elements of a character vector x into substrings according to the presence of substring split within them.

Usage

strsplit(x, split, extended = TRUE, fixed = FALSE, perl = FALSE)

Arguments

x	character vector, each element of which is to be split. Other inputs, including a factor, will give an error.
split	character vector (or object which can be coerced to such) containing regular expression(s) (unless fixed = TRUE) to use for splitting. If empty matches occur, in particular if split has length 0, x is split into single characters. If split has length greater than 1, it is re-cycled along x.
extended	logical. If TRUE (the default), extended regular expression matching is used, and if FALSE basic regular expressions are used.
fixed	logical. If TRUE match split exactly, otherwise use regular expressions. Has priority over perl and extended.
perl	logical. Should perl-compatible regexps be used? Has priority over extended.

Details

Argument split will be coerced to character, so you will see uses with split = NULL to mean split = character(0), including in the examples below.

Note that splitting into single characters can be done via split=character(0) or split=""; the two are equivalent. The definition of ‘character’ here depends on the locale (and perhaps OS): in a single-byte locale it is a byte, and in a multi-byte locale it is the unit represented by a ‘wide character’ (almost always a Unicode point).

A missing value of split does not split the corresponding element(s) of x at all.

The algorithm applied to each input string is

    repeat {
        if the string is empty
            break.
        if there is a match
            add the string to the left of the match to the output.
            remove the match and all to the left of it.
        else
            add the string to the output.
            break.
    }
  

Note that this means that if there is a match at the beginning of a (non-empty) string, the first element of the output is "", but if there is a match at the end of the string, the output is the same as with the match removed.

Value

A list of length length(x) the i-th element of which contains the vector of splits of x[i].

If fixed = TRUE or perl = TRUE and if any element of x or split is declared to be in UTF-8 (see Encoding, non-ASCII character strings in the result will be in UTF-8 and have the encoding declared as UTF-8. Otherwise they will be in the current locale's encoding, and be declared to have the encoding of the current locale if either Latin-1 or UTF-8 and the corresponding input had a declared encoding.

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 perl = TRUE seems much faster and more reliable for such usages.

The perl = TRUE option is only implemented for single-byte and UTF-8 encodings, and will warn if used in a non-UTF-8 multibyte locale.

See Also

paste for the reverse, grep and sub for string search and manipulation; further nchar, substr.

‘regular expression’ for the details of the pattern specification.

Examples

noquote(strsplit("A text I want to display with spaces", NULL)[[1]])

x <- c(as = "asfef", qu = "qwerty", "yuiop[", "b", "stuff.blah.yech")
# split x on the letter e
strsplit(x,"e")

unlist(strsplit("a.b.c", "."))
## [1] "" "" "" "" ""
## Note that 'split' is a regexp!
## If you really want to split on '.', use
unlist(strsplit("a.b.c", "\\."))
## [1] "a" "b" "c"
## or
unlist(strsplit("a.b.c", ".", fixed = TRUE))

## a useful function: rev() for strings
strReverse <- function(x)
        sapply(lapply(strsplit(x, NULL), rev), paste, collapse="")
strReverse(c("abc", "Statistics"))

## get the first names of the members of R-core
a <- readLines(file.path(R.home("doc"),"AUTHORS"))[-(1:8)]
a <- a[(0:2)-length(a)]
(a <- sub(" .*","", a))
# and reverse them
strReverse(a)

## Note that final empty strings are not produced:
strsplit(paste(c("", "a", ""), collapse="#"), split="#")[[1]]
# [1] ""  "a"
## and also an empty string is only produced before a definite match:
strsplit("", " ")[[1]]    # character(0)
strsplit(" ", " ")[[1]]   # [1] ""

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