WordPress：カテゴリ別のタグクラウドを出す方法

タグクラウドをそのまま設置すると、そのサイトで利用されているタグが全て表示されますが、特定カテゴリ以下で利用されているタグを表示する方法になります。

function.php へ記述

function my_category_tag_cloud($args) {
  $defaults = array(
    'smallest' => 8, 'largest' => 22, 'unit' => 'pt', 'number' => 45,
    'format' => 'flat', 'separator' => "\n", 'orderby' => 'name', 'order' => 'ASC',
    'exclude' => '', 'include' => '', 'link' => 'view', 'taxonomy' => 'post_tag', 'echo' => true
  );
  $args = wp_parse_args( $args, $defaults );

  global $wpdb;
  $query = "
    SELECT DISTINCT terms2.term_id as term_id, terms2.name as name, t2.count as count
    FROM
      $wpdb->posts as p1
        LEFT JOIN $wpdb->term_relationships as r1 ON p1.ID = r1.object_ID
        LEFT JOIN $wpdb->term_taxonomy as t1 ON r1.term_taxonomy_id = t1.term_taxonomy_id
        LEFT JOIN $wpdb->terms as terms1 ON t1.term_id = terms1.term_id,
      $wpdb->posts as p2
        LEFT JOIN $wpdb->term_relationships as r2 ON p2.ID = r2.object_ID
        LEFT JOIN $wpdb->term_taxonomy as t2 ON r2.term_taxonomy_id = t2.term_taxonomy_id
        LEFT JOIN $wpdb->terms as terms2 ON t2.term_id = terms2.term_id
      WHERE
        t1.taxonomy = 'category' AND p1.post_status = 'publish' AND terms1.term_id = " . $args['cat'] . " AND
        t2.taxonomy = 'post_tag' AND p2.post_status = 'publish'
        AND p1.ID = p2.ID
  ";
  $tags = $wpdb->get_results($query);
  foreach ( $tags as $key => $tag ) {
    if ( 'edit' == $args['link'] )
      $link = get_edit_tag_link( $tag->term_id, $args['taxonomy'] );
    else
      $link = get_term_link( intval($tag->term_id), $args['taxonomy'] );
    if ( is_wp_error( $link ) )
      return false;

    $tags[ $key ]->link = $link;
    $tags[ $key ]->id = $tag->term_id;
  }

  $return = wp_generate_tag_cloud( $tags, $args );
  $return = apply_filters( 'wp_tag_cloud', $return, $args );

  if ( 'array' == $args['format'] || empty($args['echo']) )
    return $return;

  echo $return;
}

表示させたい場所へ記述

<?php
my_category_tag_cloud('cat=5'); //表示させたいカテゴリIDを記述
?>

また下記のように記述すればカテゴリIDをベタ書きせず、開いているカテゴリに応じて動的に切り替えられます。

<?php
foreach((get_the_category()) as $cat) {
  $cat_id = $cat->cat_ID ;
    break ;
  }
$query = 'cat=' . $cat_id;
my_category_tag_cloud($query);
?>

参考元：http://ja.forums.wordpress.org/topic/3432