You gotta do what you gotta do, but your example probably doesn't do what you want in R. > system.time(vec1 <- rnorm(1000000)) user system elapsed

You gotta do what you gotta do, but your example probably doesn't do what you want in R. > system.time(vec1 <- rnorm(1000000)) user system elapsed 0.200 0.000 0.199 My computer takes .2 seconds to generate the million random normals and assign them to vec1. > vec1 = rnorm(1000000) > system.time(vec1) user system elapsed 0 0 0 My computer only takes 0 seconds to evaluate the existing vec1 of length one million.