Display tags from specific category in select fields

Question

I am looking to display all tags in select form that are from posts that have been assigned to a specific category.

I am using the following code to generate every tag in a select form

<div>
<?php
echo "<select onChange=\"document.location.href=this.options[this.selectedIndex].value;\">";
echo "<option>By product</option>\n";
foreach (get_tags() as $tag)
{
  echo "<option value=\"";
  echo get_tag_link($tag->term_id);
  echo "\">".$tag->name."</option>\n";
}
      echo "</select>"; ?>
</div>

Can someone point me in the direction on how I can just display the tags that are from all posts assigned to the videos category?

Any help much appreciated

Answer 1

From my understanding of the question and your comment:

I want to display all tags that are from posts that have been assigned to the specific category

You would first need to get all the posts that have that tag assigned, loop through said posts and save the unique tags to an array. Finally, loop through the array and display them in the select list. The only thing you would need to do on your end is replace $reltaed_term_id = 7 with whatever the ID is of the tag you're looking to target.

<?php
    $reltaed_term_id        = 7;
    $unique_related_tags    = array();

    $related = new WP_Query( array(
        'post_type'     => 'post',
        'posts_per_page'=> -1,
        'fields'        => 'ids',
        'cat '          => $reltaed_term_id,
    ) );

    if( $related->have_posts() ) {
        foreach( $related->posts as $post_id ) {
            $tags = wp_get_post_tags( $post_id );
            if( ! empty( $tags ) ) {
                foreach( $tags as $tag ) {
                    if( empty( $unique_related_tags ) || ! array_key_exists( $tag->term_id, $unique_related_tags ) ) {
                        $unique_related_tags[ $tag->term_id ] = $tag->name;
                    }
                }
            }
        }

        wp_reset_postdata();
    }

    if( ! empty( $unique_related_tags ) ) :
?>

        <div>
            <select onChange="document.location.href=this.options[this.selectedIndex].value;">
                <option>By product</option>

              <?php foreach( $unique_related_tags as $tag_id => $tag_name ) : ?>

                <option value="<?php echo get_tag_link( $tag_id ); ?>"><?php echo $tag_name; ?></option>

              <?php endforeach; ?>

            </select>
        </div>

<?php endif; ?>

I haven't tested the above code so let me know if you run into issues.

Answer 2

<div>
<?php
echo "<select onChange=\"document.location.href=this.options[this.selectedIndex].value;\">";
echo "<option>By product</option>\n";
foreach (get_tags() as $tag)
{
if($tag['taxonomy']=="your_category"){
  echo "<option value=\"";
  echo get_tag_link($tag->term_id);
  echo "\">".$tag->name."</option>\n";
  }
}
      echo "</select>"; ?>
</div>

use this and put your category