I have 9 observations in a table. I want to take mean of first 3 observations, then next 3 and then last 3 in R. How do we do that?

Question

X <- c(1:9)
data <- data.frame(x)

I want a table where I get three numbers: mean(of first three) mean(of next three) mean(of last three)

Answer 1

You need to create a new variable that will be used as a group. Here's an example:

> data$group <- rep(c("a", "b", "c"), each = 3)
> aggregate(X ~ group, data = data, FUN = mean)
  group X
1     a 2
2     b 5
3     c 8