Adding to a parameter for category filtering
<p>Ok so i have a question about PHP, and  I don't know if i'm just being stupid or if this is just a lot harder than i thought :/</p>

<p>So i'm trying to filter some results down through GET parameter's in the URL. I'm thinking the best way to do this would be similar to what ebuyer.com do.</p>

<p>When you filter there search results by different category's the URl is built up like so</p>

<pre><code>filtercat=36,134,142,62 etc
</code></pre>

<p>How are they adding to the parameter whilst keeping the rest of the selected category's?</p>

<p>Help!</p>

<p><strong>I'm basically trying to create what is on <a href="http://www.ebuyer.com/search?page=1&amp;sort=relevancy&amp;limit=10&amp;q=memory+card&amp;filtercat=48,36" rel="nofollow">this site</a>, on the left sidebar where you can select and deselect filters for your search</strong></p>

<p>Many thanks for any replies</p>

<p><strong>UPDATE</strong></p>

<p>Below is some code but repeated clicking on the link causes multiple occurrences of the same value</p>

<p>e.g. categories.php?filtercat=361343636</p>

<p>how can I stop this and add commas in between so the output is?</p>

<p>e.g. categories.php?filtercat=36,134   etc</p>

<pre><code>&lt;?php 

$filter = $_GET['filtercat'];
$pieces = explode(",", $filter);
$edit_url = http_build_query( Array( 'filtercat' =&gt; ''.$pieces[0].$pieces[1].$pieces[2].'' ) ); 

echo($edit_url);
?&gt; 
</code></pre>

<p>Then in my links I have </p>

<pre><code>&lt;a href="&lt;?php echo('categories.php?'.$edit_url.'36'); ?&gt;"&gt;36catagory&lt;/a&gt; 

&lt;a href="&lt;?php echo('categories.php?'.$edit_url.'134'); ?&gt;"&gt;134catagory&lt;/a&gt;
</code></pre>

<p>The explode does not work though as there are no commas... the whole things a giant mess really and I'm so confused :/ Help!</p>
