Split loop into columns

by

Try this:

<div class="all-posts">
   <div class="post-group>
      <?php $i = 0;
      if (have_posts() ) : while ( have_posts() ) : the_post();
         if ($i%4 == 0) echo '</div><div class="post-group">'; ?>
         <div class="post">
            <?php the_title(); ?>
         </div>
         <?php $i++;
      endwhile; endif; ?>
   </div><!-- end post-group -->
</div><!-- end all-posts -->

You code was closing, opening and closing div on multiples of 4.
Anyway, I’m guessing all this is about layout, so you should be able to find a better solution only with CSS.