Get Tags Based On The WordPress Category

By: Matt on 9/15/2009
In: Wordpress
Tags: Wordpress Hacks

WordPress does a lot of things really well. Sometimes you want to do something that seems simple but requires some tweaking and a bit of hacking. If you want to get specific and display tags based on specific categories of your choosing, this code will let you do it.

<?php
	query_posts('category_name=work');
	if (have_posts()) : while (have_posts()) : the_post();
        $posttags = get_the_tags();
		if ($posttags) {
			foreach($posttags as $tag) {
				$all_tags_arr[] = $tag -> name; //USING JUST $tag MAKING $all_tags_arr A MULTI-DIMENSIONAL ARRAY, WHICH DOES WORK WITH array_unique
			}
		}
	endwhile; endif; 

	$tags_arr = array_unique($all_tags_arr); //REMOVES DUPLICATES
	echo '<pre>'.print_r($tags_arr, true).'</pre>'; //OUTPUT FINAL TAGS FROM CATEGORY

?>

Here is another method that you can use to take it even farther.

Note: If you use the code below you do not need to include the other snippet above.

In your theme’s functions.php insert the following function:

function get_category_tags($args) {
	global $wpdb;
	$tags = $wpdb->get_results
	("
		SELECT DISTINCT terms2.term_id as tag_id, terms2.name as tag_name, null as tag_link
		FROM
			wp_posts as p1
			LEFT JOIN wp_term_relationships as r1 ON p1.ID = r1.object_ID
			LEFT JOIN wp_term_taxonomy as t1 ON r1.term_taxonomy_id = t1.term_taxonomy_id
			LEFT JOIN wp_terms as terms1 ON t1.term_id = terms1.term_id,

			wp_posts as p2
			LEFT JOIN wp_term_relationships as r2 ON p2.ID = r2.object_ID
			LEFT JOIN wp_term_taxonomy as t2 ON r2.term_taxonomy_id = t2.term_taxonomy_id
			LEFT JOIN wp_terms as terms2 ON t2.term_id = terms2.term_id
		WHERE
			t1.taxonomy = 'category' AND p1.post_status = 'publish' AND terms1.term_id IN (".$args['categories'].") AND
			t2.taxonomy = 'post_tag' AND p2.post_status = 'publish'
			AND p1.ID = p2.ID
		ORDER by tag_name
	");
	$count = 0;
	foreach ($tags as $tag) {
		$tags[$count]->tag_link = get_tag_link($tag->tag_id);
		$count++;
	}
	return $tags;
}

In your theme document call the function as follows. Notice it accepts multiple category id’s:

$args = array(
	'categories'				=> '12,13,14'
);
$tags = get_category_tags($args);

This will return an array that you could do the following with:

$content .= "<ul>";
foreach ($tags as $tag) {
	$content .= "<li><a href=\"$tag->tag_link\">$tag->tag_name</a></li>";
}
$content .= "</ul>";
echo $content;

.via { WordPress Forums }