Takes a StringCounter of normalized URL and parses them into
    a list of path directories. The file name is
    included in the path directory list.

def path_dirs(urls):
    '''
    Takes a StringCounter of normalized URL and parses them into
    a list of path directories. The file name is
    included in the path directory list.
    '''
    path_dirs = StringCounter()
    for url in urls:
        for path_dir in filter(None, urlparse(url).path.split('/')):
            path_dirs[path_dir] += urls[url]
    return path_dirs