Quicksort algorithm in R to demonstrate recursion

README.md

A quicksort algorithm to demonstrate recursion. Adapted from Norman Matloff, The Art of R Programming (San Francisco: No Starch Press, 2011), 176.

quicksort.r

quicksort <- function(x) {
  if(length(x) <= 1) return(x)
  
  pivot       <- x[1]
  remainder   <- x[-1]
  remainder_1 <- remainder[remainder < pivot]
  remainder_2 <- remainder[remainder >= pivot]
  
  remainder_1 <- quicksort(remainder_1)
  remainder_2 <- quicksort(remainder_2)
  
  return(c(remainder_1, pivot, remainder_2))
}

if (require("testthat")) {
  test_that("quicksort function sorts properly", {
    x <- c(1, 6, 2, 10, -9, 12, 4, -12)
    y <- c(-12, -9, 1, 2, 4, 6, 10, 12)
    expect_that(quicksort(x), equals(y))
    expect_that(quicksort(x), equals(sort(x)))
  })
}