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JavaScript: DHTML Quick Sort

This page demonstrates the Quick Sort algorithm. This is the most advanced algorithm of the four presented, but has some problems w.r.t. speed and the fact that it is not a 'stable' sort (see link at bottom of page for details). At this stage we've found the Shell Sort algorithm to be more efficient with web data.

id	colour	random
1	blue	454
2	yellow	327
3	green	129
4	purple	799
5	green	781
6	green	241
7	red	254
8	purple	659
9	orange	765
10	green	185
11	blue	704
12	orange	436
13	red	677
14	yellow	942
15	red	413
16	orange	168
17	orange	804
18	red	568
19	yellow	231
20	yellow	165

[add rows to TABLE]

How does it work?

For a more detailed discussion on the sorting process, you can refer to the Bubble Sort page. The only difference between the two is the actual sorting algorithm, with the Quick Sort, in theory, being much faster:

  // global variables
  var col = 0;
  var parent = null;
  var items = new Array();
  var N = 0;

  function quicksort(m, n, desc)
  {
    if(n <= m+1) return;

    if((n - m) == 2) {
      if(compare(get(n-1), get(m), desc)) exchange(n-1, m);
      return;
    }

    i = m + 1;
    j = n - 1;

    if(compare(get(m), get(i), desc)) exchange(i, m);
    if(compare(get(j), get(m), desc)) exchange(m, j);
    if(compare(get(m), get(i), desc)) exchange(i, m);

    pivot = get(m);

    while(true) {
      j--;
      while(compare(pivot, get(j), desc)) j--;
      i++;
      while(compare(get(i), pivot, desc)) i++;
      if(j <= i) break;
      exchange(i, j);
    }

    exchange(m, j);

    if((j-m) < (n-j)) {
      quicksort(m, j, desc);
      quicksort(j+1, n, desc);
    } else {
      quicksort(j+1, n, desc);
      quicksort(m, j, desc);
    }
  }

  function sortTable(tableid, n, desc)
  {
    parent = document.getElementById(tableid);
    col = n;

    if(parent.nodeName != "TBODY")
      parent = parent.getElementsByTagName("TBODY")[0];
    if(parent.nodeName != "TBODY")
      return false;

    items = parent.getElementsByTagName("TR");
    N = items.length;

    // quick sort
    quicksort(0, N, desc);
  }

expand code box

This algorithm makes use of the get and compare function presented previously in the Bubble Sort demonstration, and the exchange function introduced in the Shell Sort demonstration.

The sorting functions presented so far have all been quite inefficient because they first have to read the DOM and then apply the various algorithms. To get around this limitation, each of the sorting algorithms has also been implemented using object-oriented (OOP) techniques.

All four methods (using OOP) are now available as external javascript files on the related page: DHTML Sorting Using OOP.

Other Sorting Algorithms

Advanced Code

DHTML Sorting Using OOP

References

Quicksort is broken. Is it worth fixing?

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JavaScript: DHTML Quick Sort

How does it work?

Related Articles

Other Sorting Algorithms

Advanced Code

References