How to batch convert comments to posts?

You can copy this code into a plugin and when activated will convert all comments into posts, and delete the comments (so you will not have duplicates)

You can also limit what kind of comments will be converted the posts using the parameters for get_comments ( http://codex.wordpress.org/Function_Reference/get_comments )

    register_activation_hook( __FILE__, 'wpse_29474_convert_to_posts' );
    function wpse_29474_convert_to_posts(){
        $comments = get_comments();

        foreach($comments as $comment) 
        {

            $post=get_post($comment->comment_post_ID);
            $title=sprintf("Comment on %s by %s",$post->post_title,$comment->comment_author);
            $content=$comment->comment_content;
            $my_post = array(
                 'post_title' => $title,
                 'post_content' => $content,
                 'post_status' => 'publish',
                 'post_author' => 1
            );      
           wp_insert_post( $my_post );
           wp_delete_comment( $comment->comment_ID );
        }

    }