Extract sample_stats from tfp trace.

def sample_stats_to_xarray(self):
        """Extract sample_stats from tfp trace."""
        if self.model_fn is None or self.observed is None:
            return None

        log_likelihood = []
        sample_size = self.posterior[0].shape[0]

        for i in range(sample_size):
            variables = {}
            for var_i, var_name in enumerate(self.var_names):
                variables[var_name] = self.posterior[var_i][i]

            with self.ed.interception(self._value_setter(variables)):
                log_likelihood.append((self.model_fn().distribution.log_prob(self.observed)))

        data = {}
        if self.dims is not None:
            coord_name = self.dims.get("obs")
        else:
            coord_name = None
        dims = {"log_likelihood": coord_name}

        with self.tf.Session() as sess:
            data["log_likelihood"] = np.expand_dims(
                sess.run(log_likelihood, feed_dict=self.feed_dict), axis=0
            )
        return dict_to_dataset(data, library=self.tfp, coords=self.coords, dims=dims)