# 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.

idcolourrandom
1orange558
2purple343
3orange967
4yellow664
5green741
6purple824
7orange170
8orange862
9purple971
10yellow564
11orange862
12orange945
13green607
14yellow834
15purple313
16yellow686
17red355
18yellow457
19red824
20orange273
Sort by DESC?

## 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.

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