letter: Subsetting a string
In anandhupresannan/biostrings: Efficient manipulation of biological strings

Description Usage Arguments Details Value See Also Examples

Extract a substring from a string by picking up individual letters by their position.

1	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.

subseq, XString-class, XStringViews-class, MaskedXString-class

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)