letter {Biostrings}R Documentation

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.

Details

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

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.

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)

[Package Biostrings version 2.28.0 Index]