def Marginal(self, i, name='<STR_LIT>'):
pmf = Pmf(name=name)<EOL>for vs, prob in self.Items():<EOL><INDENT>pmf.Incr(vs[i], prob)<EOL><DEDENT>return pmf<EOL>
Gets the marginal distribution of the indicated variable.

        i: index of the variable we want

        Returns: Pmf