JavaScript quicksort

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quicksort javascript github
mergesort javascript
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w3resource quicksort javascript

I have been looking around the web for a while and I am wondering if there is a 'stable' defacto implementation of quicksort that is generally used? I can write my own but why reinvent the wheel...

You can easily "stabilize" an unstable sort using a decorate-sort-undecorate pattern

function stableSort(v, f)
    if (f === undefined) {
        f = function(a, b) {
            a = ""+a; b = ""+b;
            return a < b ? -1 : (a > b ? 1 : 0);
    var dv = [];
    for (var i=0; i<v.length; i++) {
        dv[i] = [v[i], i];
    dv.sort(function(a, b){
              return f(a[0], b[0]) || (a[1] - b[1]);
    for (var i=0; i<v.length; i++) {
        v[i] = dv[i][0];

the idea is to add the index as last sorting term so that no two elements are now "the same" and if everything else is the same the original index will be the discriminating factor.

Computer science in JavaScript: Quicksort, Computer science in JavaScript: Quicksort. Find a “pivot” item in the array. Start a pointer (the left pointer) at the first item in the array. Start a pointer (the right pointer) at the last item in the array. While the value at the left pointer in the array is less than the pivot value, move the left pointer to the Write a JavaScript program to sort a list of elements using Quick sort. Quick sort is a comparison sort, meaning that it can sort items of any type for which a "less-than" relation (formally, a total order) is defined. Pictorial presentation - Quick Sort algorithm : Animated visualization of the quicksort algorithm.

  1. Put your objects into an array.
  2. Call Array.sort(). It's very fast.

    var array = [3,7,2,8,2,782,7,29,1,3,0,34];
    console.log(array); // prints [0, 1, 2, 2, 29, 3, 3, 34, 7, 7, 782, 8]

Why does that print in lexicographic order? That's how array.sort() works by default, e.g. if you don't provide a comparator function. Let's fix this.

    var array = [3,7,2,8,2,782,7,29,1,3,0,34];
    array.sort(function (a, b)
        return a-b;
    console.log(array); // prints [0, 1, 2, 2, 3, 3, 7, 7, 8, 29, 34, 782]

QuickSort Algorithm in JavaScript, Quick Sort algorithm is one of the most used and popular algorithms in any programming language. But, if you are a JavaScript developer, then  Quicksort is one of the most efficient methods for sorting an array in computer science. For a thorough breakdown, it has its own Wikipedia article. This article will cover implementing quicksort

Quicksort (recursive)

function quicksort(array) {
  if (array.length <= 1) {
    return array;

  var pivot = array[0];
  var left = []; 
  var right = [];

  for (var i = 1; i < array.length; i++) {
    array[i] < pivot ? left.push(array[i]) : right.push(array[i]);

  return quicksort(left).concat(pivot, quicksort(right));

var unsorted = [23, 45, 16, 37, 3, 99, 22];
var sorted = quicksort(unsorted);

console.log('Sorted array', sorted);

JavaScript: Sort a list of elements using Quick sort, JavaScript Searching and Sorting Algorithm exercises, practice and solution: Write a JavaScript program to sort a list of elements using Quick  In this tutorial, we are going to learn about quicksort algorithm and its implementation in JavaScript. Quicksort. it is an efficient sorting algorithm for the larger datasets where it performs faster than the merge sort and heap sort. It was Developed by a British computer scientist Tony Hoare in 1959 and published in 1961. How does quicksort works?

A Functional equivalent

In celebration of Functional Javascript, which appears to be the in thing

at the moment, especially given ES6+ wonderful syntactic sugar additions. Arrow functions and destructuring I propose a very clean, short functional equivalent of the quicksort function. I have not tested it for performance or compared it to the built-in quicksort function but it might help those who are struggling to understand the practical use of a quicksort. Given its declarative nature it is very easy to see what is happening as oppose to how it works.

Here is a JSBin version without comments,console

function quickSortF(arr) {
    // Base case
    if (!arr.length) return []

    // This is a ES6 addition, it uses destructuring to pull out the 
    // first value and the rest, similar to how other functional languages
    // such as Haskell, Scala do it. You can then use the variables as 
    // normal below
    const [head, ...tail] = arr,
          // here we are using the arrow functions, and taking full 
          // advantage of the concise syntax, the verbose version of
          // function(e) => { return e < head } is the same thing
          // so we end up with the partition part, two arrays,
          // one smaller than the pivot and one bigger than the 
          // pivot, in this case is the head variable
          left = tail.filter( e => e < head),
          right = tail.filter( e => e >= head)

       // this is the conquer bit of divide-and-conquer
       // recursively run through each left and right array
       // until we hit the if condition which returns an empty
       // array. These results are all connected using concat,
       // and we get our sorted array.
       return quickSortF(left).concat(head, quickSortF(right))           


const q7 = quickSortF([11,8,14,3,6,2,7]) 
//[2, 3, 6, 7, 8, 11, 14]
const q8 =  quickSortF([11,8,14,3,6,2,1, 7])
//[1, 2, 3, 6, 7, 8, 11, 14]
const q9 = quickSortF([16,11,9,7,6,5,3, 2])
//[2, 3, 5, 6, 7, 9, 11, 16]


The comments should provide enough if it is already not clear what is happening. The actual code is very short without comments, and you may have noticed I am not a fan of the semicolon. :)

Understanding Quick Sort via JavaScript ←, Using JavaScript, learn one of the most popular and professional sorting algorithms: quick sort. In this blog which has pointed out that Array.sort is implemented in quicksort or merge sort internaly. Quicksort is generally considered to be efficient and fast and so is used by V8 as the implementation for Array.prototype.sort() on arrays with more than 23 items.

In this blog which has pointed out that Array.sort is implemented in quicksort or merge sort internaly.

Quicksort is generally considered to be efficient and fast and so is used by V8 as the implementation for Array.prototype.sort() on arrays with more than 23 items. For less than 23 items, V8 uses insertion sort[2]. Merge sort is a competitor of quicksort as it is also efficient and fast but has the added benefit of being stable. This is why Mozilla and Safari use it for their implementation of Array.prototype.sort().

and when using Array.sort,you should return -1 0 1 instead of true or false in Chrome.

  return a<b;
// maybe--> [21, 0, 3, 11, 4, 5, 6, 7, 8, 9, 10, 1, 2, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22]
  return a > b ? -1 : a < b ? 1 : 0;
// --> [22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

QuickSort.js · GitHub, Find a "pivot" element in the array to compare all other. // elements against and then shift elements before or after. // pivot depending on their  The quicksort() function accepts three arguments, the array to sort, the index where the left pointer should start, and the index where the right pointer should start. To optimize for performance, the array isn’t sorted if it has zero or one items. If there are two or more items in the array then it is partitioned.

JS: Sorting Algorithm, Call Quick sort: Pass the array and pass left and right to the quickSort function. For the first call, left would be the index of the first element which  The Quicksort algorithm Definition. Quicksort is a divide and conquer algorithm. Quicksort first divides a large array into two smaller sub-arrays: the low elements and the high elements. Quicksort can then recursively sort the sub-arrays. From Wikipedia. Visualization

JavaScript quicksort, You can easily "stabilize" an unstable sort using a decorate-sort-undecorate pattern function stableSort(v, f) { if (f === undefined) { f = function(a, b) { a = ""+a;  The purpose of this post is to present a possible animation of Quicksort algorithm using JavaScript. Quicksort is a practical and fast sorting algorithm. Quicksort is a practical and fast sorting algorithm.

Quick Sort, A quick implementation in JavaScript: const arr = [6, 2, 5, 3, 8, 7, 1, 4] const quickSort = (arr, start, end) => { if(start < end) { // You can learn about how the pivot  The sort () method sorts the items of an array. The sort order can be either alphabetic or numeric, and either ascending (up) or descending (down). By default, the sort () method sorts the values as strings in alphabetical and ascending order. This works well for strings ("Apple" comes before "Banana"). However, if numbers are sorted as strings

  • be careful using the JavaScript .Sort(); ECMAscript standard does not specify which sort algorithm is to be used, so different browsers implement different sort algorithms
  • Indeed which was why i was going to write my own.
  • Just FYI, if you write your own it will be definitely a lot slower than a native method. Do you absolutely need stable sorting?
  • BTW, you ask for a "stable" implementation of quicksort, but quicksort is not an inherently stable sort. Efficient implementations will not be stable.
  • Also why do you care if it's quicksort or not? Looks like merge sort is becoming the defacto…
  • ...Though this could be more space-efficient by pushing/popping elements, and just storing i separately.
  • This is far slower than this…
  • call Array.sort(function (a, b){return a - b;}); to sort numerically.
  • this is not guaranteed stable sort, it is browser implementation specific
  • Matt, as K Ivanov stated array.sort is browser dependent and cannot be guaranteed. I was looking for some code that I would have complete control over.
  • @flavour404: If you want to have complete control, write your own function.
  • Btw Wikipedia says: Quicksort (also known as "partition-exchange sort") is a comparison sort and, in efficient implementations, is not a stable sort. (edit: just saw that you also commented this on the OP's question ;))
  • returning b-a or a-b is even faster, since Array.sort use a compare to 0 then the only the sign of the returned value (…) .
  • What is the purpose of "temp" in each if block?
  • @elad.chen that's true. I think, I forgot it there for no reason. Thanks for noticing.