Adding a thread sort option

[darnoldy]

I want to be able to sort threads within a forum by prefix (if the forum has prefixes)?not just choose to only show threads with a particular prefix.

So, I modified the showthread template like this:

PHP Code:

<select name="sort" id="sel_sort">
    .
    .
    .
    <if condition="$prefix_options">
        <option value="prefixid" $sort[prefixid]>Region</option>
    </if>
</select> 


but its not sorting.

So, is "prefixid" just the wrong variable, or do I need to add some code (with a plugin?) to process it?