ttshowcase custom shortcode

//Funtion to retrieve a message with the ratings of a particular taxonomy
add_shortcode( 'show-testimonials-custom', 'ttshowcase_get_reviews' );
function ttshowcase_get_reviews($atts) {

	 $tsargs = array(
        'post_type' => 'ttshowcase',
        'tax_query' => array(
			array(
				'taxonomy' => 'ttshowcase_groups',
				'field'    => 'slug',
				'terms'    => $atts['slug'],
			),
		),

      );

      //perform the query
      $tts_query = new WP_Query( $tsargs );

      //store the ratings in an array
      $collection = array(

      	'0' => 0,
      	'1' => 0,
      	'2' => 0,
      	'3' => 0,
      	'4' => 0,
      	'5' => 0

      	);

      $total = 0;

      while ( $tts_query->have_posts() ) : $tts_query->the_post();

      	//get rating value;
		$rating = get_post_meta( get_the_ID(), '_aditional_info_rating', true );

		//add it to collection array
		$collection[$rating] = $collection[$rating]+1;


		$total++;


      endwhile;

      $output = '';

      foreach ($collection as $key => $value) {
      		//show only if there were ratings with that value
      		if($value>0) {
      			//build output
      			$output .= 'Rating '.$key.' = '.$value.' times <br>';
      		}

      }

	  //add total rating count
      $output .= 'Total ratings:'.$total;

      return $output;

}