Help finishing a custom post type loop with custom taxonomy shortcode

Hi all, I’m desperately trying to figure out why this shortcode I created to display a custom post type which can be filtered by a custom taxonomy which I’m placing within the shortcode attributes to work.

The code can be found below:

/*******************************************************/
/* Portfolio Posts Extraction
/*******************************************************/

//define shortcode
function project_shortcode( $atts ) {
	extract( shortcode_atts( array(
		'limit' => '10',
		'orderby' => 'date',
		'catID' => 'seo',
	), $atts ) );
	// Creating custom query to fetch the project type custom post.
	//query_posts(array('post_type'=>'videos', 'tax_query' => array( array('field' => 'slug', 'terms' => array( 'adult' ),'operator' => 'NOT IN',),)  ));

	//get categories function

	if( $categories ) {

			$categories = explode( ',', $categories );

			foreach ( $categories as $i => $category ) {

				$category_slugs[$i] .= get_term( $category, 'portfolios-categories' )->slug;

			}

			$categories = implode( ',', $category_slugs );

			$args = array_merge( $args, array( 'portfolios-categories' => esc_attr( $categories ) ) );

		}

//$loop = array('post_type' => 'portfolio', 'tax_query' => array( array( 'taxonomy' => 'portfolios-category','field' => 'slug', 'terms' => '5')	) );
//$loop = new WP_Query( $args );

$loop = new WP_Query(array('post_type' => 'portfolio', 'taxonomy' => 'portfolios-categories', 'field' => 'slug', 'terms' => 'seo', 'posts_per_page' => $limit, 'orderby' => $orderby));

   // Looping through the posts and building the HTML structure.
	if($loop){

		while ($loop->have_posts()){
			$post_thumbnail_img = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'portfolio-one-fourth' );
				$post_thumbnail_data = dbh_get_the_post_thumbnail_data( $post->ID );

			 $loop->the_post();
			 $output .= '<div class="span4"> <div class="easyBox">'; 

			if( has_post_thumbnail() ) {
				//get post thumbnail
				$output .= ( $single_url ? '<a href="' . esc_url( $single_url ) . '" target="' . esc_attr( $single_target ) . '">' : null );
				$output .= get_the_post_thumbnail( get_the_ID(), 'full', array('class' => 'photo') );
				$output .= ( $single_url ? '</a>' : null );
				}

			 $output .=' <div class="contenthover">
                <a href="/"><span class="entypo plus-squared"><i></i></span></a>
            </div>
			<div class="inner">'
			;
 			 $output .= '<a href="#"><span class="entypo monitor metaText"><i></i>website</span></a>';
			 $output .= '<h3 class="light"><a href="'.get_permalink().'">'. get_the_title().'</a></h3>';
			 $output .= '<div class="entry-content">'.get_the_excerpt().'</div></div><div></div></div></div>';
		}
	}
	else
		$output = 'Sorry, No portfolio items yet. Come back Soon.';
	// Now we are returning the HTML code back to the place from where the shortcode was called.
	return $output;
}
add_shortcode('projects','project_shortcode');

So basically, I want to add this shortcode: [projects catID="seo"] to display only projects that have the category under the “portfolio-categories” custom taxonomy.

Any help is truly appreciated! Thanks in advance for your help!