I have the following vector:
x = c(1, 2, 3, 10, 20, 30)
At each index, 3 consecutive elements are summed, resulting in the following vector:
c(6, 15, 33, 60)
Thus, first element is 1 + 2 + 3 = 6, the second element is 2 + 3 + 10 = 15, et.c
What you have is a vector, not an array. You can use rollapply function from zoo package to get what you need.
> x <- c(1, 2, 3, 10, 20, 30)
> #library(zoo)
> rollapply(x, 3, sum)
[1] 6 15 33 60
Take a look at ?rollapply for further details on what rollapply does and how to use it.