Exclude empty fields from custom field calculation (Average)

Question

I'm using some code I found online to calculate the average value across all posts for [a_custom_field].

Does anyone know how to exclude (from calculation) any instances where the custom field = 0 or if the custom field has not been filled in? Or maybe there's a better method to get the same result.

    global $wp_query;
        $real_query = $wp_query->query; //save reall query
        //create new query for all posts of the tag/category/whatever
        $args = array_merge( $wp_query->query, array( 'posts_per_page' => '-1' ) );

        $average_q = new WP_Query($args);
        $price_count = 0;
        $total_price = 0;
        while ($average_q->have_posts()){
        $average_q->the_post();
        $total_price = $total_price + get_post_meta($post->ID,'60mins',true);
        $price_count = $price_count + 1;}

        wp_reset_query();
        $average = $total_price / $price_count; 


        echo 'The average is' . round($average);
        query_posts($real_query);

Answer 1

Just tell the loop to continue if the custom field is 0 or blank.

if ((get_post_meta($post->ID,'60mins',true))||/*however it returns as blank*/)
{
    continue;
}

This will prevent it from being factored into the average.