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JavaScript: DHTML Shell Sort

This page demonstrates the Shell Sort algorithm. This appears to be the most efficient algorithm out of the four presented on this site. That may be because of faults in the implementation of the Quick Sort algorithm (see related link on that page for details), but until that's confirmed you probably want to use the shell sort.

id	colour	random
1	orange	729
2	yellow	735
3	red	195
4	blue	351
5	yellow	577
6	yellow	420
7	purple	714
8	yellow	593
9	blue	335
10	orange	407
11	purple	651
12	red	917
13	green	256
14	blue	463
15	yellow	158
16	green	190
17	orange	649
18	red	968
19	red	656
20	red	919

[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 Insertion Sort, in theory, being a little bit faster:

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

  function isort(m, k, desc)
  {
    for(var j=m+k; j < N; j+= k) {
      for(var i=j; i >= k && compare(get(i), get(i-k), desc); i-= k) {
        exchange(i, i-k);
      }
    }
  }

  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;

    // shell sort
    if((k = Math.floor(N/5)) > 7) {
      for(var m=0; m < k; m++) isort(m, k, desc);
    }

    if((k = Math.floor(N/7)) > 7) {
      for(var m=0; m < k; m++) isort(m, k, desc);
    }

    for(k=7; k > 0; k -= 2) {
      for(var m=0; m < k; m++) isort(m, k, desc);
    }
  }

Interestingly, the Shell Sort algorithm actually makes use of the previously presented Insertion Sort algorithm.

New exchange function

Because the Shell Sort algorithm requires non-adjacent items to be swapped, we need to make some changes to the exchange function that was previously used for both the Bubble Sort and Insertion Sort. The get and compare functions remain unchanged.

  function exchange(i, j)
  {
    if(i == j+1) {
      parent.insertBefore(items[i], items[j]);
    } else if(j == i+1) {
      parent.insertBefore(items[j], items[i]);
    } else {
      var tmpNode = parent.replaceChild(items[i], items[j]);
      if(typeof(items[i]) == "undefined") {
        parent.appendChild(tmpNode);
      } else {
        parent.insertBefore(tmpNode, items[i]);
      }
    }
  }

For an even more advanced sorting technique, see the Quick Sort demonstration.

Other Sorting Algorithms

Advanced Code

DHTML Sorting Using OOP

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JavaScript: DHTML Shell Sort

How does it work?

New exchange function

Related Articles

Other Sorting Algorithms

Advanced Code

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