R vs Julia sorting

R_sort.R

fastsort <- function(x, partial) {
  y <- if (length(partial) <= 10L) {
    partial <- .Internal(qsort(partial, FALSE))
    .Internal(psort(x, partial))
  }
  else {
    .Internal(qsort(x, FALSE))
  }
  y
}

sim2 <- function(n, k, m, iters) {
  f <- function(i) {
    x1 <- x2 <- runif(n)
    x2[1:m] <- runif(m)
    x.top1 <- fastsort(x1, partial=(n-k+1):n)[(n-k+1):n]
    x.top2 <- fastsort(x2, partial=(n-k+1):n)[(n-k+1):n]
    return(sum(match(x.top2, x.top1, nomatch = 0) > 0))
  }
  v <- sapply(seq_len(iters), f)
  sum(k*iters, -v)/iters
}

n <- 10
k <- 4
m <- 1

set.seed(1)
system.time(print(sim(n, k, m, 1e6)))
#> [1] 0.617969
#>   user  system elapsed 
#> 34.990   0.156  35.239
set.seed(1)
system.time(print(sim2(n, k, m, 1e6)))
#> [1] 0.617969
#>   user  system elapsed 
#> 10.892   0.073  11.010