An untested proof of concept solution to grouping events by day and ordering them by venue (upstairs & downstairs )

date-venue-group.php

<?php
   /**
    * An untested proof of concept solution to grouping events by day and ordering them by venue
    * (upstairs & downstairs )
    * @see http://wp-event-organiser.com/forums/topic/returning-2-events-for-a-single-date-based-on-venue/
    * @todo Change first three lines as appropriate
   */

   $upstairs_id   = 1; //Set to venue ID of upstairs venue
   $downstairs_id = 2; //Set to venue ID of downstairs venue

   $events = eo_get_events(array(...)); //Set this to the desired query
   
   $num_events = count( $events );
   $key        = 0;

   while( $key < $num_events ){

      $event      = $events[$key];
      $next_event = isset( $events[$key + 1] ) ? $events[$key + 1] : false;

      $date = eo_get_the_start( DATETIMEOBJ, $event->ID, null, $event->occurrence_id );

      $key++; //Increment key

      if( !$next_event ){

         //No next event - just show this one, is it upstairs or downstairs?
         $event_venue_id   = eo_get_venue( $event->ID );
         $upstairs_event   = ( $event_venue_id == $upstairs_id ? $event : false );
         $downstairs_event = ( $event_venue_id == $downstairs_id ? $event : false );

      }elseif( eo_get_the_start( 'Y-m-d', $event->ID, null, $event->occurrence_id ) != eo_get_the_start( 'Y-m-d', $next_event->ID, null, $next_event->occurrence_id ) ){

         //This event is on a different day to the next event, so ignore the next event for now
         $upstairs_event   = ( $event_venue_id == $upstairs_id ? $event : false );
         $downstairs_event = ( $event_venue_id == $downstairs_id ? $event : false );

      }else{

         //This event is on the same day to the next event
         $upstairs_event   = ( $event_venue_id == $upstairs_id ? $next_event : $event );
         $downstairs_event = ( $event_venue_id == $downstairs_id ? $event : $next_event );

         //Increment key again has we're showing two events on this iteration.
         $key++;

      }
      ?>
      <div>
         <h3> <?php echo 'Events on date '.$date->format('jS F Y' );?> </h3>

         <!-- Upstairs -->
         <div class="upstairs">
            <?php if( $upstairs_event ): ?>
               <?php echo get_the_title( $upstairs_event->ID ); ?>
            <?php endif; ?>
         </div>

         <div class="downstairs">
            <?php if( $downstairs_event ): ?>
               <?php echo get_the_title( $downstairs_event->ID ); ?>
            <?php endif; ?>
         </div>

      </div>
      <?php           

    }