Why is seq(x) so much slower than 1:length(x)?

Question

I recently answered a question pertaining to for loops. Upon testing my code\'s speed, I noticed that the use of seq() as opposed to :

Answer 1

Using seq_len you get nearly the same time as the : operator:

f3 <- function(){
  x <- 1:5; y <- numeric(length(x))
  for(i in seq_len(length(x))) y[i] <- x[i]^2
  y
}

library(microbenchmark)
microbenchmark(f1(), f2(),f3())

Unit: microseconds
 expr    min      lq  median     uq    max neval
 f1()  9.988 10.6855 10.9650 11.245 50.704   100
 f2() 23.257 23.7465 24.0605 24.445 88.140   100
 f3() 10.127 10.5460 10.7555 11.175 18.857   100

Internally seq is doing many verifications before calling : or seq_len.