nchar Count the Number of Characters (or Bytes or Width)

Description

nchar takes a character vector as an argument and returns a vector whose elements contain the sizes of the corresponding elements of x. Internally, it is a generic, for which methods can be defined (see InternalMethods).

nzchar is a fast way to find out if elements of a character vector are non-empty strings.

Usage

nchar(x, type = "chars", allowNA = FALSE, keepNA = NA)

nzchar(x, keepNA = FALSE)

Arguments

x	character vector, or a vector to be coerced to a character vector. Giving a factor is an error.
type	character string: partial matching to one of c("bytes", "chars", "width"). See ‘Details’.
allowNA	logical: should NA be returned for invalid multibyte strings or "bytes"-encoded strings (rather than throwing an error)?
keepNA	logical: should NA be returned when x is NA? If false, nchar() returns 2, as that is the number of printing characters used when strings are written to output, and nzchar() is TRUE. The default for nchar(), NA, means to use keepNA = TRUE unless type is "width".

Details

The ‘size’ of a character string can be measured in one of three ways (corresponding to the type argument):

bytes

The number of bytes needed to store the string (plus in C a final terminator which is not counted).

chars

The number of characters.

width

The number of columns cat will use to print the string in a monospaced font. The same as chars if this cannot be calculated.

These will often be the same, and almost always will be in single-byte locales (but note how type determines the default for keepNA). There will be differences between the first two with multibyte character sequences, e.g. in UTF-8 locales.

The internal equivalent of the default method of as.character is performed on x (so there is no method dispatch). If you want to operate on non-vector objects passing them through deparse first will be required.

Value

For nchar, an integer vector giving the sizes of each element. For missing values (i.e., NA, i.e., NA_character_), nchar() returns NA_integer_ if keepNA is true, and 2, the number of printing characters, if false.

type = "width" gives (an approximation to) the number of columns used in printing each element in a terminal font, taking into account double-width, zero-width and ‘composing’ characters. The approximation is likely to be poor when there are unassigned or non-printing characters.

If allowNA = TRUE and an element is detected as invalid in a multi-byte character set such as UTF-8, its number of characters and the width will be NA. Otherwise the number of characters will be non-negative, so !is.na(nchar(x, "chars", TRUE)) is a test of validity.

A character string marked with "bytes" encoding (see Encoding) has a number of bytes, but neither a known number of characters nor a width, so the latter two types are NA if allowNA = TRUE, otherwise an error.

Names, dims and dimnames are copied from the input.

For nzchar, a logical vector of the same length as x, true if and only if the element has non-zero length; if the element is NA, nzchar() is true when keepNA is false (the default) and NA otherwise.

Note

This does not by default give the number of characters that will be used to print() the string. Use encodeString to find that. Where character strings have been marked as UTF-8, the number of characters and widths will be computed in UTF-8, even though printing may use escapes such as <U+2642> in a non-UTF-8 locale.

The concept of ‘width’ is a slippery one even in a monospaced font. Some human languages have the concept of combining characters, in which two or more characters are rendered together: an example would be "y\u306", which is two characters of width one: combining characters are given width zero, and there are other zero-width characters such as the zero-width space "\u200b".

Some East Asian languages have ‘wide’ characters, ideographs which are conventionally printed across two columns when mixed with ASCII and other ‘narrow’ characters in those languages. The problem is that whether a computer prints wide characters over two or one columns depends on the font, with it not being uncommon to use two columns in a font intended for East Asian users and a single column in a ‘Western’ font. Unicode has encodings for ‘fullwidth’ versions of ASCII characters and ‘halfwidth’ versions of Katakana (Japanese) and Hangul (Korean) characters. Then there is the ‘East Asian Ambiguous class’ (Greek, Cyrillic, signs, some accented Latin chars, etc), for which the historical practice was to use two columns in East Asia and one elsewhere. The width quoted by nchar for characters in that class (and some others) depends on the locale, being one except in some East Asian locales on some OSes (notably Windows).

Control characters are given width zero in multi-byte locales, but are usually given width one in single-byte ones (as their positions are often undefined and maybe re-used as in CP1252 vs Latin-1).

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

Unicode Standard Annex #11: East Asian Width. https://www.unicode.org/reports/tr11/

See Also

strwidth giving width of strings for plotting; paste, substr, strsplit

Examples

x <- c("asfef", "qwerty", "yuiop[", "b", "stuff.blah.yech")
nchar(x)
# 5  6  6  1 15

nchar(deparse(mean))
# 18 17  <-- unless mean differs from base::mean

x[3] <- NA; x
nchar(x, keepNA= TRUE) #  5  6 NA  1 15
nchar(x, keepNA=FALSE) #  5  6  2  1 15
stopifnot(identical(nchar(x     ), nchar(x, keepNA= TRUE)),
          identical(nchar(x, "w"), nchar(x, keepNA=FALSE)),
          identical(is.na(x), is.na(nchar(x))))

##' nchar() for all three types :
nchars <- function(x, ...)
   vapply(c("chars", "bytes", "width"),
          function(tp) nchar(x, tp, ...), integer(length(x)))

nchars("\u200b") # in R versions (>= 2015-09-xx):
## chars bytes width
##     1     3     0

data.frame(x, nchars(x)) ## all three types : same unless for NA
## force the same by forcing 'keepNA':
(ncT <- nchars(x, keepNA = TRUE)) ## .... NA NA NA ....
(ncF <- nchars(x, keepNA = FALSE))## ....  2  2  2 ....
stopifnot(apply(ncT, 1, function(.) length(unique(.))) == 1,
          apply(ncF, 1, function(.) length(unique(.))) == 1)