# JavaScript: DHTML Shell Sort

This page demonstrates the Shell Sort algorithm which appears to be the most efficient algorithm out of the four presented on this site.

That may be due to 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
1green852
2orange664
3red297
4blue877
5orange661
6green70
7red388
8green248
9blue809
10green121
11purple727
12orange476
13orange124
14green571
15orange339
16yellow369
17blue296
18green480
19blue567
20blue516

## 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"); 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.

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