Sorting a list alphabetically with a modulus

Question

I don't have any trouble grabbing a list of elements and sorting them alphabetically, but I'm having difficulty understanding how to do it with a modulus.

### UPDATE ###

Here's the code working 'my way', however, I like the re-usability of the answer provided below more, so have accepted that answer.

<script type="text/javascript">
$(document).ready( function() {
    $('.sectionList2').each( function() {
        var oldList = $('li a', this),
            columns = 4,
            newList = [];
        for( var start = 0; start < columns; start++){
            for( var i = start; i < oldList.length; i += columns){
                newList.push('<li><a href="' + oldList[i].href + '">' + $(oldList[i]).text() + '</a></li>');
            }
        }
        $(this).html(newList.join(''));
    });
});
</script>

For example. Say I have the following unordered list:

<ul>
    <li><a href="~">Boots</a></li>
    <li><a href="~">Eyewear</a></li>
    <li><a href="~">Gloves</a></li>
    <li><a href="~">Heated Gear</a></li>
    <li><a href="~">Helmet Accessories</a></li>
    <li><a href="~">Helmets</a></li>
    <li><a href="~">Jackets</a></li>
    <li><a href="~">Mechanic's Wear</a></li>
    <li><a href="~">Pants</a></li>
    <li><a href="~">Protection</a></li>
    <li><a href="~">Rainwear</a></li>
    <li><a href="~">Random Apparel</a></li>
    <li><a href="~">Riding Suits</a></li>
    <li><a href="~">Riding Underwear</a></li>
    <li><a href="~">Socks</a></li>
    <li><a href="~">Vests</a></li>
</ul>

I have this list set to display in 4 columns with each li floated right. Visually this makes finding items in larger lists difficult. The output I need is this:

<ul>
    <li><a href="~">Boots</a></li>
    <li><a href="~">Helmet Accessories</a></li>
    <li><a href="~">Pants</a></li>
    <li><a href="~">Riding Suits</a></li>
    <li><a href="~">Eyewear</a></li>
    <li><a href="~">Helmets</a></li>
    <li><a href="~">Protection</a></li>
    <li><a href="~">Riding Underwear</a></li>
    <li><a href="~">Gloves</a></li>
    <li><a href="~">Jackets</a></li>
    <li><a href="~">Rainwear</a></li>
    <li><a href="~">Socks</a></li>
    <li><a href="~">Heated Gear</a></li>
    <li><a href="~">Mechanic's Wear</a></li>
    <li><a href="~">Random Apparel</a></li>
    <li><a href="~">Vests</a></li>
</ul>

What I'm looking for is a function that I can pass my array of list items and get my array returned, sorted alphabetically, with a modulus of choice; in this case 4.

Any help would be appreciated as I can find no documentation on the subject.

Answer 1

1. Alphabetize your list. This is already done, in your case, but if not:

   function alphabetizeElements(a, b)
   {
       var aText = $(a).text();
       var bText = $(b).text();
       return aText > bText ? 1 : aText < bText ? -1 : 0;
   }
   var alphabetizedList = $("#myList li").sort(alphabetizeElements);
   

2. Store the alphabetized index of each element:

   $.each(alphabetizedList, function(i)
   {
       $(this).data("alphaIndex", i);
   });
   

3. Sort the alphabetized list by modulus first, then index:

   function listColumnSortFn(columns)
   {
       return function(a, b)
       {
           var aIndex = $(a).data("alphaIndex");
           var bIndex = $(b).data("alphaIndex");
           return ((aIndex % columns) - (bIndex % columns)) || (aIndex - bIndex);
       }
   }
   var columnSortedList = alphabetizedList.sort(listColumnSortFn(4));
   

4. Replace the list elements with your sorted elements:

   $("#myList li").remove();
   $("#myList").append(columnSortedList);
   

Here is the whole thing, all together:

function sortList(columns)
{
    var alphabetizedList = $("#myList li").sort(alphabetizeElements);
    $.each(alphabetizedList, function(i)
    {
        $(this).data("alphaIndex", i);
    });
    var columnSortedList = alphabetizedList.sort(listColumnSortFn(columns));
    $("#myList li").remove();
    $("#myList").append(columnSortedList);
}
function alphabetizeElements(a, b)
{
    var aText = $(a).text();
    var bText = $(b).text();
    return aText > bText ? 1 : aText < bText ? -1 : 0;
}
function listColumnSortFn(columns)
{
    return function(a, b)
    {
        var aIndex = $(a).data("alphaIndex");
        var bIndex = $(b).data("alphaIndex");
        return ((aIndex % columns) - (bIndex % columns)) || (aIndex - bIndex);
    }
}
$(function()
{
    sortList(4);
});