Substrings of a Character Vector

Description

Extract or replace substrings in a character vector.

Usage

substr(x, start, stop)
substring(text, first, last = 1000000L)

substr(x, start, stop) <- value
substring(text, first, last = 1000000L) <- value

Arguments

Details

substring is compatible with S, with first and last instead of start and stop. For vector arguments, it expands the arguments cyclically to the length of the longest provided none are of zero length.

When extracting, if start is larger than the string length then "" is returned. If stop is larger than the string length then the portion until the end of the string is returned.

For the extraction functions, x or text will be converted to a character vector by as.character if it is not already one.

For the replacement functions, if start is larger than the string length then no replacement is done. If the portion to be replaced is longer than the replacement string, then only the portion the length of the string is replaced.

If any argument has an NA element, the corresponding element of the answer is NA.

Elements of the result will have the encoding declared as that of the current locale (see Encoding) if the corresponding input had a declared Latin-1 or UTF-8 encoding and the current locale is either Latin-1 or UTF-8.

If an input element has declared "bytes" encoding (see Encoding), the subsetting is done in units of bytes not characters.

Value

For substr, a character vector of the same length and with the same attributes as x (after possible coercion). start and stop are recycled as necessary.

For substring, a character vector of length the longest of the arguments. This will have names taken from x (if it has any after coercion, repeated as needed), and other attributes copied from x if it is the longest of the arguments).

For the replacement functions, a character vector of the same length as x or text, with attributes such as names preserved.

Elements of x or text with a declared encoding (see Encoding) will be returned with the same encoding.

Note

The S version of substring<- ignores last; this version does not.

These functions are often used with nchar to truncate a display. That does not really work (you want to limit the width, not the number of characters, so it would be better to use strtrim), but at least make sure you use the default nchar(type = "chars").

References

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

See Also

startsWith and endsWith; strsplit, paste, nchar.

Examples

substr("abcdef", 2, 4)
substring("abcdef", 1:6, 1:6)
## strsplit() is more efficient ...

substr(rep("abcdef", 4), 1:4, 4:5)
x <- c("asfef", "qwerty", "yuiop[", "b", "stuff.blah.yech")
substr(x, 2, 5)
substring(x, 2, 4:6)

X <- x
names(X) <- LETTERS[seq_along(x)]
comment(X) <- noquote("is a named vector")
str(aX <- attributes(X))
substring(x, 2) <- c("..", "+++")
substring(X, 2) <- c("..", "+++")
X
stopifnot(x == X, identical(aX, attributes(X)), nzchar(comment(X)))