Average of values in an array

Question

I have an array and want to build a loop which averages every second value starting at the first value of the array and after the first round the loop should start with the second value of the array.

For example:

3,6,18,10,2

The result should be:

7.666,8,10

   for 7.6666= (3+18+2)/3 
   for 8= (6+10)/2
   for 10=(18+2)/2 

Thanks in advance

Answer 1

Are you looking for something like this?

x <- c(3,6,18,10,2)

n <- length(x)
sapply(seq_len(n-2), function(X) {
    mean(x[seq(X, n, by=2)])
})
# [1]  7.666667  8.000000 10.000000

---

And then something more interesting, to earn @mnel's upvote ;)

n <- length(x)
m <- matrix(0, n, n-2)
ii <- row(m) - col(m)
m[ii >= 0 & !ii %% 2] <- 1
colSums(x * m)/colSums(m)
# [1]  7.666667  8.000000 10.000000