List all posts of certain category which share some tags

Question

My problem is quite simple:

I've got a couple of posts in different categories that have several tags, some of them in common.

When I load a post, in my sidebar (using PHP Code) I want to show a list of all the posts of another category that share the same tags as the one displayed.

I've tried related posts and it doesn't do the trick, because I found no way of adding the 'only this category' condition.

UPDATE. I have tried this

<?php
global $post;
$tagargs = $catargs= '';
$catnames ='';
$tagnames = '';
$tags = get_the_tags($id);

    if ($tags) {
        foreach ($tags as $tag) {
            $tagnames .= $tag->name . ',';
        }
        $tagargs = array(
            'ignore_sticky_posts' => 1,
            'tag' => $tagnames,
            'post__not_in' => array($id),
            'showposts' => $number,
            'orderby' => 'name',
            'order' => 'asc',
            'cat' => '152'
        );
    }

$posts = get_posts($tagargs);
  foreach($posts as $post) :
    ?>
    <li><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></li>
 <?php endforeach; ?>

And I get all the posts in category 152 (the one I want) but that have only in common the first tag. I have figured out how to do the opposite, I mean, first, get the tags of all the posts inside this category (152) and then compare them with those in the current post (because sometimes, the current post have more than two or three), and get those posts that have all the tags in both sides. What do you think?

Answer 1

First, you want to get the tags that the post in question already has. To do this, use <?php wp_get_post_tags( $post_id, $args ) ?>

Then use WP_Query to grab the posts that have the tag in question:

$query = new WP_Query( '$post_id' );

Here is a sample of how it might work by creating a shortcode to put in your sidebar:

**
 * List Posts by tag.
 *
 * By Matt McFarland  10/23/2013
 * Use as a shortcode [posts_by_tag tag_id={TAG ID} or tag_slug = {SLUG}]
 * Available options are in the shortcode_atts below, non-empty is default
 * examples
 *                  [posts_by_tag amount="4" tag="cars"]
 *                  [posts_by_tag amount="6" tag_id="34"]
 *                  [posts_by_tag tag="cars"]  (amount is 6 by default)
 */
 add_shortcode('posts_by_tag','mm_list_posts_by_tag');
 function mm_list_posts_by_tag($atts) {

    ob_start();
    extract( shortcode_atts( array(
        'amount'        => '6',
        'tag'               => '',
        'tag_id'            => '',
        'orderby'       => 'post_date',
        'order'         => 'DESC',
        'key'               => '',
        'meta_key'      => '',
        'post_type'     => 'post',
        'post_status'   => 'publish', 
    ), $atts ) );       
    $args = array(
        'posts_per_page'   => esc_attr($amount),
        'tag'               => esc_attr($tag),
        'tag_id'            => esc_attr($tag_id),
        'orderby'       => esc_attr($orderby),
        'order'         => esc_attr($order),
        'key'               => esc_attr($key),
        'meta_key'      => esc_attr($meta_key),
        'post_type'     => esc_attr($post_type),
        'post_status'   => esc_attr($post_status));
        $tag_posts = new WP_Query($args); ?>
    <?php if ( $tag_posts->have_posts() ) : ?>  
        <div class="taglist-container">
            <ul>
                <?php while ( $tag_posts->have_posts() ) : $tag_posts->the_post(); ?>
                    <li>
                        <strong><a href="<?php the_permalink(); ?>" rel="bookmark"><?php search_title_highlight(); ?></a></strong>
                        <?php echo human_time_diff( get_the_time('U'), current_time('timestamp') ) . ' ago'; ?>
                    </li>
                <?php endwhile; ?>
            </ul>
        </div>
    <?php endif; 
    $result = ob_get_clean(); 
    return $result;     
}