[R] Measuring CPU time

[. .]

Why time is increasing for the same operation?

I was expecting +/- the same time for each n.

Thanks in advance.

bench <- function(f1, n, ...) {
  t <- 0
  for(i in 1:n) {
    func <- function(x) x^2
    expr <- list(...)[1]
    f1 <- c("system.time(y <- ", gsub("XXX",expr,f1),")[3]")
    t1 <- eval(parse(text = f1))
    printf("time %d: %f\n", i, t1)
    t <- t + t1
  }
  t <- t/n
  printf("mean time: %f", t)
}
bench("func(XXX)", 10, "1:100")