Subsetting a string
Extract a substring from a string by picking up individual letters by their position.
letter(x, i)
x |
A character vector, or an XString, XStringViews or MaskedXString object. |
i |
An integer vector with no NAs. |
Unlike with the substr or substring functions,
i must contain valid positions.
A character vector of length 1 when x is an XString
or MaskedXString object (the masks are ignored for the latter).
A character vector of the same length as x when x
is a character vector or an XStringViews object.
Note that, because i must contain valid positions,
all non-NA elements in the result are guaranteed to have exactly
length(i) characters.
x <- c("abcd", "ABC")
i <- c(3, 1, 1, 2, 1)
## With a character vector:
letter(x[1], 3:1)
letter(x, 3)
letter(x, i)
#letter(x, 4) # Error!
## With a BString object:
letter(BString(x[1]), i) # returns a character vector
BString(x[1])[i] # returns a BString object
## With an XStringViews object:
x2 <- as(BStringSet(x), "Views")
letter(x2, i)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.