How can I vectorize access to neighbour vector elements in R?

Question

I have the following vector

 v = c(F, F, F, T, F, F, F, F, F, T, F, F, F)

How can I change v so that the previous 2 elements and the following

Answer 1

This sort of thing is probably as vectorized as you're going to get:

v[unlist(sapply(which(v),function(x) {x + c(-2,-1,1,2)},simplify = FALSE))] <- TRUE
> v
 [1] FALSE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE

But note that you haven't specified what should happen in the TRUE elements are near the ends of your vector. That would require more work. Nor do you specify what happens if there are two TRUE elements that are closer than two positions from each other.

Alternatively:

v[outer(which(v),c(-2,-1,1,2),"+")] <- TRUE
> v
 [1] FALSE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE

At a basic level, we're doing the same thing here, but the second option is certainly more compact, although possibly harder to understand.