Group posts by taxonomy.

group-by-tax.php

<?php
	$get_current_cat = get_term_by('name', single_cat_title('',false), 'category');
	$current_cat = $get_current_cat->term_id;


	// List posts by the terms for a custom taxonomy of any post type
	$post_type = 'special_events';
	$tax = 'locations';
	$tax_terms = get_terms( $tax, 'orderby=name&order=ASC');
	if ($tax_terms) {
		foreach ($tax_terms  as $tax_term) {
			$args = array(
				'post_type'			=> $post_type,
				"$tax"				=> $tax_term->slug,
				'post_status'		=> 'publish',
				'posts_per_page'	=> -1
			);

			$my_query = null;
			$my_query = new WP_Query($args);

			if( $my_query->have_posts() ) : ?>

				<div class="clearfix">

					<div class="btn-group bootstrap-select shortcode-dropdown-lists">
					
					<button type="button" class="btn dropdown-toggle" data-toggle="dropdown">
						<span class="filter-option pull-left"><?php echo $tax_term->name; ?></span> <span class="caret"></span>
					</button>
					
					<ul class="dropdown-menu" role="menu">

					<?php while ( $my_query->have_posts() ) : $my_query->the_post(); ?>

						<?php $term_list = wp_get_post_terms($post->ID, 'category', array("fields" => "ids")); ?>
						
						<?php if (in_array($current_cat, $term_list) ): ?>

    							<li><?php the_title(); ?></li>

						<?php endif; // if in_array ?>
						
					<?php endwhile; // end of loop ?>
					
					</ul>
					
					</div>
					
				</div>

			<?php endif; // if have_posts()
			wp_reset_query();

		} // end foreach #tax_terms
	} // end if tax_terms
?>