How can I replace vector values in a sequence at regular intervals in R?

Question

I am trying to replace values of a vector of sequence 1 to 100, such that after every 3 elements, the next 2 are replaced by 0s. for example:

a<-1:20

I want it to be like this:

a <- c(1, 2, 3, 0, 0, 6, 7, 8, 0, 0, 11, 12, 13, 0, 0, 16, 17, 18, 0, 0)

is there a way to do this automatically?

thanks for any help

Answer 1

We can use rep with a recycling logical vector to assign values in certain positions to 0

a[rep(c(FALSE, TRUE), c(3,2))]  <- 0
a
#[1]  1  2  3  0  0  6  7  8  0  0 11 12 13  0  0 16 17 18  0  0