R: Split the Elements of a Character Vector

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 as “split”. 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`, extended regular expression matching is used, and if `FALSE` basic regular expressions are used.
`fixed`	logical. If `TRUE` match string 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 spltting 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].

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.

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] ""

[Package base version 2.4.1 Index]