Ruby quicksort

gistfile1.txt

module Enumerable
  def quicksort()
    if size <= 1
      self
    else
      pivot = shift
      lower, greater = partition {|x| x < pivot }.map(&:quicksort)
      lower.push(pivot).concat(greater)
    end
  end
end

hm, the following JS port does not work. it returns a strangely scrambled list with one member less.

function quicksort(list) {
  if (list.length <= 1) {
    return list;
  }
  else {
    var pivot = list.shift();
    var lower = list.filter(function(element) {
      return element < pivot;
    });
    var upper = list.filter(function(element) {
      return element > pivot;
    });
    lower.push(pivot) //.concat(upper);
    return lower.concat(upper);
  }
}

/* quicksort([23,74,2,8,21,2,9]) =>[ 2,
  8,
  21,
  2,
  9,
  23,
  74 ]

> quicksort([2,1,3])
[ 1, 2, 3 ]
> quicksort([4,1,3,2])
[ 1, 3, 2, 4 ]
*/

You need >= in the upper check, otherwise if the pivot is duplicated, then the other values that are the same will be dropped.