small fix to posterior_to_xarray (#262)

* small fix to posterior_to_xarray

* autopep8

arviz/data/io_pymc3.py

@@ -5,6 +5,7 @@
 from arviz.data.inference_data import InferenceData
 from .base import requires, dict_to_dataset, generate_dims_coords
 
+
 class PyMC3Converter:
     """Encapsulate PyMC3 specific logic."""
 
@@ -24,7 +25,7 @@ def _extract_log_likelihood(self):
         """
         # This next line is brittle and may not work forever, but is a secret
         # way to access the model from the trace.
-        model = self.trace._straces[0].model # pylint: disable=protected-access
+        model = self.trace._straces[0].model  # pylint: disable=protected-access
         if len(model.observed_RVs) != 1:
             return None, None
         else:
@@ -34,6 +35,7 @@ def _extract_log_likelihood(self):
                 coord_name = None
 
         cached = [(var, var.logp_elemwise) for var in model.observed_RVs]
+
         def log_likelihood_vals_point(point):
             """Compute log likelihood for each observed point."""
             log_like_vals = []
@@ -54,18 +56,19 @@ def log_likelihood_vals_point(point):
     def posterior_to_xarray(self):
         """Convert the posterior to an xarray dataset."""
         import pymc3 as pm
-        var_names = pm.utils.get_default_varnames(self.trace.varnames, # pylint: disable=no-member
+        var_names = pm.utils.get_default_varnames(self.trace.varnames,  # pylint: disable=no-member
                                                   include_transformed=False)
         data = {}
         for var_name in var_names:
-            data[var_name] = np.array(self.trace.get_values(var_name, combine=False))
+            data[var_name] = np.array(self.trace.get_values(var_name, combine=False,
+                                                            squeeze=False))
         return dict_to_dataset(data, coords=self.coords, dims=self.dims)
 
     @requires('trace')
     def sample_stats_to_xarray(self):
         """Extract sample_stats from PyMC3 trace."""
         rename_key = {
-            'model_logp' : 'lp',
+            'model_logp': 'lp',
         }
         data = {}
         for stat in self.trace.stat_names:
@@ -98,7 +101,7 @@ def observed_data_to_xarray(self):
         """Convert observed data to xarray."""
         # This next line is brittle and may not work forever, but is a secret
         # way to access the model from the trace.
-        model = self.trace._straces[0].model # pylint: disable=protected-access
+        model = self.trace._straces[0].model  # pylint: disable=protected-access
 
         observations = {obs.name: obs.observations for obs in model.observed_RVs}
         if self.dims is None:
@@ -116,7 +119,6 @@ def observed_data_to_xarray(self):
             observed_data[name] = xr.DataArray(vals, dims=val_dims, coords=coords)
         return xr.Dataset(data_vars=observed_data)
 
-
     def to_inference_data(self):
         """Convert all available data to an InferenceData object.