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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	677
2	orange	314
3	yellow	136
4	purple	763
5	green	237
6	blue	967
7	blue	108
8	green	997
9	yellow	405
10	green	313
11	green	815
12	blue	959
13	yellow	954
14	red	972
15	purple	166
16	blue	861
17	orange	538
18	blue	766
19	purple	232
20	orange	774

[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.

References

Quicksort is broken. Is it worth fixing?

DHTML Quick Sort [JAVASCRIPT]
DHTML Sorting Using OOP [JAVASCRIPT]
DHTML Sorting Using OOP - Example 1 [JAVASCRIPT]
DHTML Insertion Sort [JAVASCRIPT]
DHTML Bubble Sort [JAVASCRIPT]
DHTML Shell Sort [JAVASCRIPT]
Sorting Arrays of Arrays [PHP]
Sorting SimpleXMLElement Object arrays [PHP]

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JavaScript: DHTML Quick Sort

JavaScript: DHTML Quick Sort

How does it work?

References

Related Articles - Sorting Algorithms

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