docs: def gamma(ranks_list1,ranks_list2):
      '''
      Goodman and Kruskal's gamma correlation coefficient
      :param ranks_list1: a list of ranks (integers)
      :param ranks_list2: a second list of ranks (integers) of equal length with corresponding entries
      :return: Gamma correlation coefficient (rank correlation ignoring ties)
      '''
      num_concordant_pairs = 0
      num_discordant_pairs = 0
      num_tied_x = 0
      num_tied_y = 0
      num_tied_xy = 0
      num_items = len(ranks_list1)
      for i in range(num_items):
          rank_1 = ranks_list1[i]
          rank_2 = ranks_list2[i]
          for j in range(i + 1, num_items):
              diff1 = ranks_list1[j] - rank_1
              diff2 = ranks_list2[j] - rank_2
              if (diff1 > 0 and diff2 > 0) or (diff1 < 0 and diff2 < 0):
                  num_concordant_pairs += 1
              elif (diff1 > 0 and diff2 < 0) or (diff1 < 0 and diff2 > 0):
                  num_discordant_pairs += 1
              elif diff1 == 0 and diff2 == 0:
                  num_tied_xy += 1
              elif diff1 == 0:
                  num_tied_x += 1
              elif diff2 == 0:
                  num_tied_y += 1
      try:
          gamma_corr_coeff = float(num_concordant_pairs - num_discordant_pairs)/float(num_concordant_pairs + num_discordant_pairs)
      except:
          gamma_corr_coeff = 'n/a'
      return [num_tied_x, num_tied_y, num_tied_xy, gamma_corr_coeff]