/*----------------------------------------------------------------------------------*/
/* Popular Post in functions.php
/*----------------------------------------------------------------------------------*/
function getPostViews($postID){
    $count_key = 'post_views_count';
    $count = get_post_meta($postID, $count_key, true);
    if($count==''){
        delete_post_meta($postID, $count_key);
        add_post_meta($postID, $count_key, '0');
        return "0 View";
    }
    return $count.' Views';
}

function setPostViews($postID) {
    $count_key = 'post_views_count';
    $count = get_post_meta($postID, $count_key, true);
    if($count==''){
        $count = 0;
        delete_post_meta($postID, $count_key);
        add_post_meta($postID, $count_key, '0');
    }else{
        $count++;
        update_post_meta($postID, $count_key, $count);
    }
}

/*------------------------------------------------------------------------*/
/* Set post views in single.php
/*------------------------------------------------------------------------*/
setPostViews(get_the_ID());

/*------------------------------------------------------------------------*/
/* Loop in index.php
/*------------------------------------------------------------------------*/
<?php $newspopularpost = new WP_Query( array( 'category_name = news','meta_key= post_views_count', 'orderby= meta_value_num', 'order= DESC' ) );
if ( $newspopularpost -> have_posts() ) : while ( have_posts() -> the_post); ?>

<a href="<?php the_permalink() ?>" title="<?php the_title(); ?>"><h1><?php the_title(); ?></h1></a>
<?php the_excerpt(); ?>

<?php endif; ?>
<?php wp_reset_query(); ?>
/* Wash, rinse, repeat for each of the 6 primary categories */