Relvanssi - sorting by meta value & hits filter

gistfile1.php

add_filter('relevanssi_modify_wp_query', 'start_date_filter');
function start_date_filter($query) {
  
    $query->set('orderby', 'departure');
    $query->set('order', 'asc');
    return $query;
 
}

// Sort by meta field
add_filter('relevanssi_hits_filter', 'order_the_results');
function order_the_results($hits) {
	
    global $wp_query;
	 
	switch ( $wp_query->query_vars['orderby'] ) {
			
		case 'departure':
		        
            $dates = array();
	    		
	    	foreach ($hits[0] as $hit) {
	        	
	        	$startdate = get_post_meta( $hit->ID, 'start_date', true );
		       	if ( !isset( $dates[$startdate] ) ) $dates[$startdate] = array();
	    	   	array_push($dates[$startdate], $hit);
	    	    		
	        }
	 
			if ($wp_query->query_vars['order'] == 'asc') {
			
				ksort($dates);
				
			} else {
				
				krsort($dates);
				
			}
	 
            $sorted_hits = array();
				
			foreach ($dates as $startdate => $year_hits) {
	   	     	
                $sorted_hits = array_merge($sorted_hits, $year_hits);
		        
            }
				
			$hits[0] = $sorted_hits;
			
		    break;
	 	 
		case 'relevance':
			
			//do nothing
			break;
	 
	}
		 
    return $hits;
	    
}

Thanks for the note. This saved my day!