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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sem(self, ddof=1):
 """ Compute standard error of the mean of groups, excluding missing values. For multiple groupings, the result index will be a MultiIndex. Parameters ddof : integer, default 1 degrees of freedom """


        return self.std(ddof=ddof) / np.sqrt(self.count())