WordPress Category Dropdown Nav

functions-category-dropdown.php

<?php
/**
 * Category Dropdown. Can be used for listing categories on WP archive pages.
 */
?>
<select onchange="this.options[this.selectedIndex].value && (window.location = this.options[this.selectedIndex].value);">
  <option value="<?php echo get_permalink( get_option( 'page_for_posts' ) ) ?>">All</option>
  <?php
    $cats = get_categories();
    $current_category = get_category( get_query_var( 'cat' ) );
    foreach ($cats as $key => $cat)
      echo '<option '. ( $cat->cat_ID === $current_category->cat_ID ? 'selected' : '' ) .' value="' . get_category_link( $cat->cat_ID ) . '">' . $cat->name . '</option>';
  ?>
</select>