We can use
rep to add 53 to the
vector ('vN2') after finding the number of observations for each year.
vN2 + rep(c(0, 53), tapply(vN2, cumsum(c(TRUE, diff(vN2) < 0)), FUN = length))
set.seed(24) vN <- rep(1:53, sample(1:5, 53, replace=TRUE)) vN1 <- rep(1:53, sample(1:6, 53, replace=TRUE)) vN2 <- c(vN, vN1)