strsplit {base}

Split the Elements of a Character Vector

Description

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

Usage

strsplit(x, split, fixed = FALSE, perl = FALSE, useBytes = 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.

fixed

logical. If TRUE match split exactly, otherwise use regular expressions. Has priority over perl.

perl

logical. Should Perl-compatible regexps be used?

useBytes

logical. If TRUE the matching is done byte-by-byte rather than character-by-character, and inputs with marked encodings are not converted. This is forced (with a warning) if any input is found which is marked as "bytes" (see Encoding).

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: 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 code 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.

Note also that if there is an empty match at the beginning of a non-empty string, the first character is returned and the algorithm continues with the rest of the string. This needs to be kept in mind when designing the regular expressions. For example, when looking for a word boundary followed by a letter ("[[:<:]]" with perl = TRUE), one can disallow a match at the beginning of a string (via "(?!^)[[:<:]]").

Invalid inputs in the current locale are warned about up to 5 times.

Value

A list of the same length as x, the i-th element of which contains the vector of splits of x[i].

If any element of x or split is declared to be in UTF-8 (see Encoding), all non-ASCII character strings in the result will be in UTF-8 and have their encoding declared as UTF-8. (This also holds if any element is declared to be Latin-1 except in a Latin-1 locale.) For perl = TRUE, useBytes = FALSE all non-ASCII strings in a multibyte locale are translated to UTF-8.

If any element of x or split is marked as "bytes" (see Encoding), all non-ASCII character strings created by the splitting in the result will be marked as "bytes", but encoding of the resulting character strings not split is unspecified (may be "bytes" or the original). If no element of x or split is marked as "bytes", but useBytes = TRUE, even the encoding of the resulting character strings created by splitting is unspecified (may be "bytes" or "unknown", possibly invalid in the current encoding). Mixed use of "bytes" and other marked encodings is discouraged, but if still desired one may use iconv to re-encode the result e.g. to UTF-8 with suitably substituted invalid bytes.

See Also

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

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

Option PCRE_use_JIT controls the details when perl = TRUE.

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] ""