functions/postdropdown.php

<?php
function display_post_selectbox($class_name='') {
    global $wpdb, $post;
    $table_prefix = $wpdb->prefix;
    $the_output = NULL;
    $last_posts = (array)$wpdb->get_results("
        SELECT {$table_prefix}terms.name, {$table_prefix}terms.term_id
        FROM {$table_prefix}terms, {$table_prefix}term_taxonomy
        WHERE {$table_prefix}terms.term_id = {$table_prefix}term_taxonomy.term_id
                AND {$table_prefix}term_taxonomy.taxonomy = 'category'
        {$hide_check}
    ");
    if (empty($last_posts)) {
        return NULL;
    }
    $used_cats = array();;
    $i = 0;
    foreach ($last_posts as $posts) {
        if (in_array($posts->name, $used_cats)) {
            unset($last_posts[$i]);
        } else {
            $used_cats[] = $posts->name;
        }
        $i++;
    }
    $last_posts = array_values($last_posts);
    $the_output .= '<select name="wordpress_posts" class="'.$class_name.'">';
    foreach ($last_posts as $posts) {
      $the_output .= '<optgroup label="'.apply_filters('list_cats', $posts->name, $posts).'">';
          $where = apply_filters('getarchives_where', "WHERE post_type = 'post' AND post_status = 'publish'" , $r );
          $arcresults = $wpdb->get_results("SELECT * FROM $wpdb->posts WHERE post_type = 'post' AND post_status = 'publish' AND ID IN (Select object_id FROM {$table_prefix}term_relationships, {$table_prefix}terms WHERE {$table_prefix}term_relationships.term_taxonomy_id =" . $posts->term_id . ") ORDER BY post_date DESC");
      foreach ( $arcresults as $arcresult ) {
           $the_output .= '<option label="'.apply_filters('the_title', $arcresult->post_title).'" value="'.apply_filters('the_title', $arcresult->post_title).'">'.apply_filters('the_title', $arcresult->post_title) . '</option>';
       }
          $the_output .= '</optgroup>';
       }
       $the_output .= '</select>';
       return $the_output;
};
?>