code: def cumulative_mean(self):
          
          from .. import extensions
          agg_op = "__builtin__cum_avg__"
          return SArray(_proxy = self.__proxy__.builtin_cumulative_aggregate(agg_op))
docs: Return the cumulative mean of the elements in the SArray.
  
          Returns an SArray where each element in the output corresponds to the
          mean value of all the elements preceding and including it. The SArray
          is expected to be of numeric type (int, float), or a numeric vector
          type.
  
          Returns
          -------
          out : Sarray[float, array.array]
  
          Notes
          -----
           - Missing values are ignored while performing the cumulative
             aggregate operation.
           - For SArray's of type array.array, all entries are expected to
             be of the same size.
  
          Examples
          --------
          >>> sa = SArray([1, 2, 3, 4, 5])
          >>> sa.cumulative_mean()
          dtype: float
          rows: 3
          [1, 1.5, 2, 2.5, 3]