Extract posterior samples from fit.

def posterior_to_xarray(self):
        """Extract posterior samples from fit."""
        posterior = self.posterior
        # filter posterior_predictive and log_likelihood
        posterior_predictive = self.posterior_predictive
        if posterior_predictive is None:
            posterior_predictive = []
        elif isinstance(posterior_predictive, str):
            posterior_predictive = [posterior_predictive]
        log_likelihood = self.log_likelihood
        if not isinstance(log_likelihood, str):
            log_likelihood = []
        else:
            log_likelihood = [log_likelihood]

        ignore = posterior_predictive + log_likelihood + ["lp__"]

        data = get_draws(posterior, ignore=ignore)

        return dict_to_dataset(data, library=self.pystan, coords=self.coords, dims=self.dims)