Means from a list of data frames in R

Question

I am relatively new to R and have a complicated situation to solve. I have uploaded a list of over 1000 data frames into R and called this list x. What I want to do is take

Answer 1

You can use lapply and pass indices as follows:

ids <- seq(3, 54, by=3)
out <- do.call(rbind, lapply(ids, function(idx) {
    t <- unlist(x[[idx]][, -1])
    c(mean(t), var(t))
}))