Collapsing columns
From Joomla! Documentation
A common requirement when designing web pages in Joomla! is for a module position to be removed when no modules are enabled in that position so that the space is available for other page elements. The region removed is referred to as a "collapsed column". This can be achieved using the countModules function.
For example, if you want to include a "user1" module position only if there are modules enabled in that position, then you could use this code:
<?php if ($this->countModules( 'user1' )) : ?>
<div class="user1">
<jdoc:include type="modules" name="user1" style="xhtml" />
</div>
<?php endif; ?>
Notice that the jdoc:include tag and its surrounding divs are only included if the countModules call returns a non-zero value (the PHP if statement treats zero as being false and any non-zero value as being true.
Sometimes you may want a pair of module positions to collapse either singly or together.
<?php if ($this->countModules( 'user1 or user2' )) : ?>
<div class="user1user2">
<?php if ($this->countModules( 'user1' )) : ?>
<jdoc:include type="modules" name="user1" style="xhtml" />
<?php endif; ?>
<?php if ($this->countModules( 'user2' )) : ?>
<jdoc:include type="modules" name="user2" style="xhtml" />
<?php endif; ?>
</div>
<?php endif; ?>
Notice how the region (which is styled by the CSS class "user1user2") is only output if user1 or user2 or both have at least one module enabled.
If you want a divider to separate the two module positions then you must be careful to only output the divider if both module positions have modules enabled in them. For example,
<?php if ($this->countModules( 'user1 or user2' )) : ?>
<div class="user1user2">
<?php if ($this->countModules( 'user1' )) : ?>
<jdoc:include type="modules" name="user1" style="xhtml" />
<?php endif; ?>
<?php if ($this->countModules( 'user1 and user2' )) : ?>
<div class="divider"></div>
<?php endif; ?>
<?php if ($this->countModules( 'user2' )) : ?>
<jdoc:include type="modules" name="user2" style="xhtml" />
<?php endif; ?>
</div>
<?php endif; ?>