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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	orange	32
2	green	965
3	purple	26
4	red	645
5	green	177
6	red	337
7	red	991
8	green	846
9	green	591
10	blue	650
11	orange	945
12	blue	467
13	green	523
14	yellow	646
15	blue	958
16	yellow	926
17	purple	849
18	green	734
19	yellow	428
20	yellow	119

[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