docs: def domain_user_stats():
      # type: () -> pd.Series
      """ Get number of distinct email addresses in observed domains
  
      TODO: get up to date with new projects layout
      How to build email_domain_users.csv:
  
      from collections import defaultdict
      import logging
      from common import utils as common
      import stscraper as scraper
  
      log = logging.getLogger("domain_user_stats")
      stats = defaultdict(set)
      for ecosystem in common.ECOSYSTEMS:
          urls = common.package_urls(ecosystem)
          for package_name, url in urls.items():
              log.info(package_name)
              try:
                  cs = scraper.commits(url)
              except scraper.RepoDoesNotExist:
                  continue
              for email_addr in cs["author_email"].dropna().unique():
                  if not email_addr or pd.isnull(email_addr):
                      continue
                  try:
                      user, email_domain = clean(email_addr).split("@")
                  except InvalidEmail:
                      continue
                  stats[email_domain].add(user)
      s = pd.Series({dm: len(users) for dm, users in stats.items()})
      s = s.rename("users").sort_values(ascending=False)
      s.to_csv("common/email_domain_users.csv", encoding="utf8", header=True)
      return s
      """
      fname = os.path.join(os.path.dirname(__file__), "email_domain_users.csv")
      stats = pd.read_csv(fname, header=0, squeeze=True, index_col=0)
      return stats[pd.notnull(stats.index)]