letter {Biostrings} | R Documentation |
Extract a substring from a string by picking up individual letters by their position.
letter(x, i)
x |
A character vector, a BString (or derived) object or a BStringViews object. |
i |
An NA-free numeric vector. |
Unlike with the substr
or substring
functions,
i
must contain valid positions.
A character vector of length 1 when x
is
a BString (or derived) object.
A character vector of the same length as x
when x
is a character vector or a BStringViews object.
Note that, because i
must contain valid positions,
all non-NA elements in the result are guaranted to have exactly
length(i)
characters.
subBString
,
BString-class,
BStringViews-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) # character vector BString(x[1])[i] # BString object ## With a BStringViews object x2 <- BStringViews(x, "BString") letter(x2, i)