Biostrings (version 2.40.2)

letter: Subsetting a string

Description

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

Usage

letter(x, i)

Arguments

x

A character vector, or an XString, XStringViews or MaskedXString object.

i

An integer vector with no NAs.

Value

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.

Details

Unlike with the substr or substring functions, i must contain valid positions.

See Also

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

Examples

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)