Apply function over consecutive groups in vector

Question

I want to calculate meas of three consecutive variables a vector.

Ex: Vec<-rep(1:10)

I would like the output to be like the screenshot below:

I have no idea. I must have done something wrong in excel. I want means of 1:3, 4:7, 8:10... — mad, Oct 10 '15 at 16:44

score 1 · Answer 1 · answered Oct 10 '15 at 16:44

1

We can create a grouping variable using gl and then get the mean with ave

 ave(Vec, as.numeric(gl(length(Vec), 3, length(Vec))))

answered Oct 10 '15 at 16:44

akrun

Can it be made so that the length will be 5 instead of 15? Like: 2, 5, 8, 11, 14? – mad Oct 10 '15 at 16:48
@mad The `Vec <- 1:10` If you meant to get the mean of 5 consecutive values, change the `gl` to `gl(length(Vec), 5, length(Vec))` – akrun Oct 10 '15 at 16:51

score 1 · Accepted Answer · answered Oct 11 '15 at 02:27

You can create the following function to calculate means by groups of 3 (or any other number):

   f <- function(x, k=3) 
     {
       for(i in seq(k,length(x),k)) 
         x[(i/k)] <- mean(x[(i-k+1):i]) 
      return(x[1:(length(x)/k)])
   }

f(1:15) [1] 2 5 8 11 14

2 Answers2