Shortcode code to display custom post by date range

shortcode.php

function fellows_shortcode($atts)
{

    // Extract Shortcode Attributes
    extract(shortcode_atts(
                    array(
        'range' => 'all',
                    ), $atts)
    );

    // Set up date ranges for query
    $datetime = new DateTime();
    $mq_operator = array();
    if ($range == "former") {
        $start = '19800101'; // 1st Jan 1980
        $end = $datetime->sub(new DateInterval('P1D'))->format('Ymd'); // -1 day
        $mq_operator[0] = '>=';
        $mq_operator[1] = '<=';
    } elseif ($range == "future") {
        $start = $datetime->add(new DateInterval('P1D'))->format('Ymd'); // +1 day
        $end = '21130101';
        $mq_operator[0] = '>=';
        $mq_operator[1] = '<=';
    } else {
        $start = $end = $datetime->format('Ymd');
        $mq_operator[0] = '<=';
        $mq_operator[1] = '>=';
    }

    // Put everything into the WP_Query attributes array
    // Currently set to order by lastname in descending order
    $atts = array(
        'post_status' => 'publish',
        'post_type' => array('fellow'),
        'posts_per_page' => 3,
        'meta_key' => 'fellow_lname',
        'orderby' => 'meta_value',
        'order' => 'DESC',
        'meta_query' => array(
            array(
                'key' => 'fellow_start_date',
                'value' => $start,
                'type' => 'date',
                'compare' => $mq_operator[0]
            ),
            array(
                'key' => 'fellow_end_date',
                'value' => $end,
                'type' => 'date',
                'compare' => $mq_operator[1]
            )
        )
    );

    // In case I ever decide to have paging I will include this
    $atts['paged'] = (get_query_var('paged')) ? get_query_var('paged') : 1;


    // The Query using WP_Query 
    // http://codex.wordpress.org/Class_Reference/WP_Query
    $wp_query = null;
    $wp_query = new WP_Query($atts);

    // Declare some variables
    $output = '';
    $count = 0;

    // Number of fellows returned - may use
    $post_count = $wp_query->found_posts;


    /* The Loop */
    if ($wp_query->have_posts()) {
        while ($wp_query->have_posts()) {

            $count++;
            $wp_query->the_post();

            // Using a simple {{}} templating system to keep things tidy
            $content = '<li>{PHOTO}
                          <a href="{PERMALINK}">{TITLE}</a>
                          <span class="flist_position"><a href="{PERMALINK}">{POSITION}</a></span>
                          <span class="flist_date">{START_DATE}{END_DATE}</span>
                          <span class="flist_institution">{INSTITUTION}</span>   
                          </li>';

            // Get the required fields in $parameters to fill the content template
            $parameters = array(
                'PERMALINK' => get_permalink(),
                'TITLE' => get_the_title(),
                'POSITION' => get_field('fellow_position'),
                'PROJECT' => get_field('fellow_ptitle'),
                'INSTITUTION' => get_field('fellow_institution'),
                    // add here more...
            );

            // Dates are a special case as require to be converted 
            // from YYmmdd to human readable format
            if (get_field('fellow_start_date')) {
                $sdate = DateTime::createFromFormat('Ymd', get_field('fellow_start_date'));
            }
            if (get_field('fellow_end_date')) {
                $edate = DateTime::createFromFormat('Ymd', get_field('fellow_end_date'));
            }

            if ($sdate) {
                $parameters['START_DATE'] = $sdate->format('M Y');
            }
            if ($edate) {
                $parameters['END_DATE'] = ' - ' . $edate->format('M Y');
            }

            // Another special case: Photograph, as it requires more code to pull the content
            if (get_field('fellow_photo')) {
                $attachment_id = get_field('fellow_photo');
                $size = "thumbnail"; // (thumbnail, medium, large, full or custom size)
                $parameters['PHOTO'] = wp_get_attachment_image($attachment_id['id'], $size);
            }


            // The template engine - replaces {{}} with appropriate $parameters[] value
            $finds = $replaces = array();
            foreach ($parameters as $find => $replace) {
                $finds[] = '{' . $find . '}';
                $replaces[] = $replace;
            }
            $output .= str_replace($finds, $replaces, $content);
        }
        // Wrap in UL and add classes
        $output = '<ul class="fellows fellows_' . $range . '">' . $output . '</ul>';
        return $output;
    }
}

add_shortcode('fellows', 'fellows_shortcode');