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Exercise

Timings - pre-allocation

In the previous exercise, growing the vector took around 2 seconds. How long does it take when we pre-allocate the vector? The pre_allocate() function is defined below.

n <- 30000
# Fast code
pre_allocate <- function(n) {
    x <- numeric(n) # Pre-allocate
    for(i in 1:n) 
        x[i] <- rnorm(1)
    x
}

Instructions

100 XP

The pre_allocate() function is available in your workspace.

  • Using system.time(), find how long it takes to run pre_allocate(n). Use the <- trick to store the result in the object res_allocate.