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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 date(self, proxy, how='median', n=500):
 """Date a proxy record Parameters proxy : ProxyRecord how : str How to perform the dating. 'median' returns the average of the MCMC ensemble. 'ensemble' returns a 'n' randomly selected members of the MCMC ensemble. Default is 'median'. n : int If 'how' is 'ensemble', the function will randomly select 'n' MCMC ensemble members, with replacement. Returns ------- DatedProxyRecord """

        assert how in ['median', 'ensemble']
        ens_members = self.mcmcfit.n_members()
        if how == 'ensemble':
            select_idx = np.random.choice(range(ens_members), size=n, replace=True)
        out = []
        for d in proxy.data.depth.values:
            age = self.agedepth(d)
            if how == 'median':
                age = np.median(age)
            elif how == 'ensemble':
                age = age[select_idx]
            out.append(age)
        return DatedProxyRecord(proxy.data.copy(), out)