[R] vectorized sub, gsub, grep, etc.

Thaden, John J ThadenJohnJ at uams.edu
Tue Oct 7 21:58:34 CEST 2008

R pattern-matching and replacement functions are
vectorized: they can operate on vectors of targets.
However, they can only use one pattern and replacement.
Here is code to apply a different pattern and replacement
for every target.  My question: can it be done better?

sub2 <- function(pattern, replacement, x) {
    len <- length(x)
    if (length(pattern) == 1) 
        pattern <- rep(pattern, len)
    if (length(replacement) == 1) 
        replacement <- rep(replacement, len)
    FUN <- function(i, ...) {
        sub(pattern[i], replacement[i], x[i], fixed = TRUE)
    idx <- 1:length(x)
    sapply(idx, FUN)    

X <- c("ab", "cd", "ef")
patt <- c("b", "cd", "a")
repl <- c("B", "CD", "A")
sub2(patt, repl, X)


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