xray oddity

In [15]: em1
Out[15]:
<xray.Dataset>
Dimensions:    (lat: 720, lon: 1440, time: 4)
Coordinates:
  * lat        (lat) float32 89.875 89.625 89.375 89.125 88.875 88.625 ...
  * lon        (lon) float32 -179.875 -179.625 -179.375 -179.125 -178.875 ...
  * time       (time) datetime64[ns] 2004-08-01 2004-08-02 2004-08-03 2004-08-04
Data variables:
    emissions  (time, lat, lon) float64 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ...
Attributes:
    ndays: 4

In [16]: em2
Out[16]:
<xray.Dataset>
Dimensions:    (lat: 360, lon: 720, time: 180)
Coordinates:
  * lat        (lat) float64 -89.75 -89.25 -88.75 -88.25 -87.75 -87.25 ...
  * lon        (lon) float64 -179.8 -179.2 -178.8 -178.2 -177.8 -177.2 ...
  * time       (time) datetime64[ns] 1993-01-31 1993-02-28 1993-03-31 ...
Data variables:
    emissions  (time, lat, lon) float64 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ...
Attributes:
    len_p: 180

In [17]: em1['parts'] = em1.emissions / em1.emissions.sum()

In [18]: em1
Out[18]: 
<xray.Dataset>
Dimensions:    (lat: 720, lon: 1440, time: 4)
Coordinates:
  * lat        (lat) float32 89.875 89.625 89.375 89.125 88.875 88.625 ...
  * lon        (lon) float32 -179.875 -179.625 -179.375 -179.125 -178.875 ...
  * time       (time) datetime64[ns] 2004-08-01 2004-08-02 2004-08-03 2004-08-04
Data variables:
    emissions  (time, lat, lon) float64 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ...
    parts      (time, lat, lon) float64 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ...
Attributes:
    ndays: 4
    
In [19]: em2['parts'] = em2.emissions / em2.emissions.sum()
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-19-61a0025c91ba> in <module>()
----> 1 em2['parts'] = em2.emissions / em2.emissions.sum()

/opt/anaconda/envs/py2/lib/python2.7/site-packages/xray/core/dataset.pyc in __setitem__(self, key, value)
    635             raise NotImplementedError('cannot yet use a dictionary as a key '
    636                                       'to set Dataset values')
--> 637         self.update({key: value})
    638
    639     def __delitem__(self, key):

/opt/anaconda/envs/py2/lib/python2.7/site-packages/xray/core/dataset.pyc in update(self, other, inplace)
   1418         """
   1419         return self.merge(
-> 1420             other, inplace=inplace, overwrite_vars=list(other), join='left')
   1421
   1422     def merge(self, other, inplace=False, overwrite_vars=set(),

/opt/anaconda/envs/py2/lib/python2.7/site-packages/xray/core/dataset.pyc in merge(self, other, inplace, overwrite_vars, compat, join)
   1477
   1478         replace_vars, new_vars, new_coord_names = merge(
-> 1479             self, other, overwrite_vars, compat=compat, join=join)
   1480
   1481         newly_coords = new_coord_names & (set(self) - set(self.coords))

/opt/anaconda/envs/py2/lib/python2.7/site-packages/xray/core/dataset.pyc in _merge_dict(self, other, overwrite_vars, compat, join)
    202     other.update(zip(alignable, aligned[1:]))
    203
--> 204     return _merge_expand(aligned_self, other, overwrite_vars, compat)
    205
    206

/opt/anaconda/envs/py2/lib/python2.7/site-packages/xray/core/dataset.pyc in _merge_expand(aligned_self, other, overwrite_vars, compat)
    174     possible_conflicts = dict((k, v) for k, v in aligned_self._variables.items()
    175                               if k not in overwrite_vars)
--> 176     new_vars, new_coord_names = _expand_variables(other, possible_conflicts, compat)
    177     replace_vars = aligned_self._variables.copy()
    178     replace_vars.update(new_vars)

/opt/anaconda/envs/py2/lib/python2.7/site-packages/xray/core/dataset.pyc in _expand_variables(raw_variables, old_variables, compat)
    142                     add_variable(dim, coord.variable)
    143             var = var.variable
--> 144         add_variable(name, var)
    145
    146     return new_variables, new_coord_names

/opt/anaconda/envs/py2/lib/python2.7/site-packages/xray/core/dataset.pyc in add_variable(name, var)
    122
    123     def add_variable(name, var):
--> 124         var = _as_dataset_variable(name, var)
    125         if name not in variables:
    126             variables[name] = var

/opt/anaconda/envs/py2/lib/python2.7/site-packages/xray/core/dataset.pyc in _as_dataset_variable(name, var)
     66     """
     67     try:
---> 68         var = as_variable(var, key=name)
     69     except TypeError:
     70         raise TypeError('Dataset variables must be an array or a tuple of '

/opt/anaconda/envs/py2/lib/python2.7/site-packages/xray/core/variable.pyc in as_variable(obj, key, strict)
     49             obj = Variable(obj.name, obj)
     50         elif key is not None:
---> 51             obj = Variable(key, obj)
     52         else:
     53             raise TypeError('cannot infer Variable dimensions')

/opt/anaconda/envs/py2/lib/python2.7/site-packages/xray/core/variable.pyc in __init__(self, dims, data, attrs, encoding, fastpath)
    194         """
    195         self._data = _as_compatible_data(data, fastpath=fastpath)
--> 196         self._dims = self._parse_dimensions(dims)
    197         self._attrs = None
    198         self._encoding = None

/opt/anaconda/envs/py2/lib/python2.7/site-packages/xray/core/variable.pyc in _parse_dimensions(self, dims)
    302             raise ValueError('dimensions %s must have the same length as the '
    303                              'number of data dimensions, ndim=%s'
--> 304                              % (dims, self.ndim))
    305         return dims
    305         return dims
    306

ValueError: dimensions ('parts',) must have the same length as the number of data dimensions, ndim=3

In [20]: