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

If x is a list of 1000 dataframes, you can use lapply to return the means and variances of a subset of this list.

ix = seq(1, 1000, 3)
lapply(x[ix], function(df){
    #exclude the first column
    c(mean(df[,-1]), var(df[,-1]))
})

Answer 2

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))
}))