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I used the comment meta to add a simple rating system. The user can post a rate from the comment form from where I added 3 dropdown comment meta.

The rating is working well, reflecting the ratings together with the comment written by the user. My only problem now is this: how can I get the average of all the ratings posted? I need the average to be placed on the post content.

My rating system rates the following:

  • Price,
  • Packaging,
  • Quality.

I want an average for each rate:

  • Average Price Rate,
  • Average Packaging Rate, and
  • Average Quality Rate.

Thank you so much!

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And please: Don't forget to vote and later accept an answer as solution. –  kaiser May 9 '11 at 13:57
Did you able to get a solution? –  Sisir Dec 29 '11 at 20:52

3 Answers 3

I've got something similar using a custom query to calculate the average on the fly - per Rabino's comment, it would be more efficient to store the result of this function as a meta value, but I'd want it triggered when a comment is approved, rather than when a comment is saved.

here's your function:

function average_rating() {
    global $wpdb;
    $post_id = get_the_ID();
    $ratings = $wpdb->get_results("

        SELECT $wpdb->commentmeta.meta_value
        FROM $wpdb->commentmeta
        INNER JOIN $wpdb->comments on $wpdb->comments.comment_id=$wpdb->commentmeta.comment_id
        WHERE $wpdb->commentmeta.meta_key='rating' 
        AND $wpdb->comments.comment_post_id=$post_id 
        AND $wpdb->comments.comment_approved =1

    $counter = 0;
    $average_rating = 0;    
    if ($ratings) {
        foreach ($ratings as $rating) {
            $average_rating = $average_rating + $rating->meta_value;
        //round the average to the nearast 1/2 point
        return (round(($average_rating/$counter)*2,0)/2);  
    } else {
        //no ratings
        return 'no rating';

In my context I have a 1-5 rating. no results of the query means no ratings provided.

Drop the following in the loop and you're good to go:

<?php echo average_rating(); ?>
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If you need to show the averages in the content, you need to pre-calculate them (before showing the comments).

My approach would be having a custom meta in the post with the calculated averages and modify those metas every time a new comment (rating) is saved.

Something like

add_action("comment_post", "wpse16733_updateAVGs");

function wpse16733_updateAVGs($comment_ID, $approved){

    if ($approved){
        $commentdata=get_comment($comment_ID, ARRAY_A); 

        (... get your rating, get post meta, calc and save ...)

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Probably you should do the inverse on comment deletion, if that apply to your case. –  MZAweb May 9 '11 at 15:22
Probably faster than my solution. +1 :) –  kaiser May 9 '11 at 16:07
This should be accepted - its much more efficient doing the calculations only when comments are added/removed, rather than every time a particular page loads –  acSlater May 19 at 16:15

This is a solution which will display the average after the last comment. As a workaround you could simply do two have_comments() comments loops and calculate the average rating with the first loop and display the comments with the second loop.

 * You need to place this function inside your comments callback function, so it get's
 * triggered with every displayed comment inside the have_comments() loop.
function wpse16733_get_comment_meta_avrg()
$divider = (int) $GLOBALS['wp_query']->comment_count;

// initial static values - these get counted up everytime the function get's triggered
static $price = 0;
static $packaging = 0;
static $quality = 0;
static $current_comment = 0;

$current_comment = (int) $current_comment++;

// receive all comment meta data
$all_meta = get_comment_meta( get_comment_ID(), '' );

// Now get the ratings (it could also be `$avrg_xy = $all_meta->rating` if an object)
$price = (int) $price + (int) $all_meta['price'];
$packaging = (int) $packaging + (int) $all_meta['packaging'];
$quality = (int) $quality + (int) $all_meta['quality'];

// calculate within the last comment
if ( $current_comment == $divider ) 
    $average['price'] = $price / $divider;
    $average['packaging'] = $packaging / $divider;
    $average['quality'] = $quality / $divider;

// now do stuff with the $average array
foreach ( $average as $rating )
    echo 'This is the average rating: '.$rating;
share|improve this answer
Note that the function is not tested. If you try it and it fails, please write a detailed description in here. If you can solve it yourself, please edit my Q with the working code, so others searching for a solution will also profit from the A. –  kaiser May 9 '11 at 13:59

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