scalar_level in MultiIndex

xarray/core/dataset.py

@@ -27,8 +27,7 @@
                     merge_data_and_coords)
 from .utils import (Frozen, SortedKeysDict, maybe_wrap_array, hashable,
                     decode_numpy_dict_values, ensure_us_time_resolution)
-from .variable import (Variable, as_variable, IndexVariable,
-                       broadcast_variables)
+from .variable import Variable, as_variable, IndexVariable, broadcast_variables
 from .pycompat import (iteritems, basestring, OrderedDict,
                        integer_types, dask_array_type, range)
 from .options import OPTIONS
@@ -576,21 +575,16 @@ def _replace_vars_and_dims(self, variables, coord_names=None, dims=None,
         return obj
 
     def _replace_indexes(self, indexes):
+        """
+        Make some index_level to scalar_level.
+        indexes: mapping from dimension name to new index.
+        """
         if not len(indexes):
             return self
         variables = self._variables.copy()
         for name, idx in indexes.items():
-            variables[name] = IndexVariable(name, idx)
-        obj = self._replace_vars_and_dims(variables)
-
-        # switch from dimension to level names, if necessary
-        dim_names = {}
-        for dim, idx in indexes.items():
-            if not isinstance(idx, pd.MultiIndex) and idx.name != dim:
-                dim_names[dim] = idx.name
-        if dim_names:
-            obj = obj.rename(dim_names)
-        return obj
+                variables[name] = variables[name].reset_levels(idx.names)
+        return self._replace_vars_and_dims(variables)
 
     def copy(self, deep=False):
         """Returns a copy of this dataset.
@@ -627,7 +621,7 @@ def _level_coords(self):
         for cname in self._coord_names:
             var = self.variables[cname]
             if var.ndim == 1:
-                level_names = var.to_index_variable().level_names
+                level_names = var.all_level_names
                 if level_names is not None:
                     dim, = var.dims
                     level_coords.update({lname: dim for lname in level_names})
@@ -1127,10 +1121,7 @@ def isel(self, drop=False, **indexers):
         Dataset.isel_points
         DataArray.isel
         """
-        invalid = [k for k in indexers if k not in self.dims]
-        if invalid:
-            raise ValueError("dimensions %r do not exist" % invalid)
-
+        indexers = indexing.get_dim_pos_indexers(self, indexers)
         # all indexers should be int, slice or np.ndarrays
         indexers = [(k, (np.asarray(v)
                          if not isinstance(v, integer_types + (slice,))
@@ -1607,6 +1598,9 @@ def expand_dims(self, dim, axis=None):
         If dim is already a scalar coordinate, it will be promoted to a 1D
         coordinate consisting of a single value.
 
+        If dim is a scalar-level of MultiIndex, this level is changed to
+        index-level.
+
         Parameters
         ----------
         dim : str or sequence of str.
@@ -1629,6 +1623,12 @@ def expand_dims(self, dim, axis=None):
 
         if isinstance(dim, basestring):
             dim = [dim]
+        else:
+            dim = list(dim)
+        # scalars to converted to index-level
+        scalars = [d for d in dim if d in self._level_coords]
+        dim = [d for d in dim if d not in scalars]
+
         if axis is not None and not isinstance(axis, (list, tuple)):
             axis = [axis]
 
@@ -1653,7 +1653,8 @@ def expand_dims(self, dim, axis=None):
         variables = OrderedDict()
         for k, v in iteritems(self._variables):
             if k not in dim:
-                if k in self._coord_names:  # Do not change coordinates
+                if k in self._coord_names:
+                    # Do not change coordinates
                     variables[k] = v
                 else:
                     result_ndim = len(v.dims) + len(axis)
@@ -1682,6 +1683,13 @@ def expand_dims(self, dim, axis=None):
                 # it will be promoted to a 1D coordinate with a single value.
                 variables[k] = v.set_dims(k)
 
+        # Convert scalar-level of MultiIndex to index-level
+        for k, v in iteritems(self._variables):
+            if v.scalar_level_names is not None and len(scalars) > 0:
+                level_dims = [s for s in scalars if s in
+                              v.scalar_level_names] + list(v.dims)
+                variables[k] = v.set_dims(level_dims)
+
         return self._replace_vars_and_dims(variables, self._coord_names)
 
     def set_index(self, append=False, inplace=False, **indexes):
@@ -1768,11 +1776,7 @@ def reorder_levels(self, inplace=False, **dim_order):
         replace_variables = {}
         for dim, order in dim_order.items():
             coord = self._variables[dim]
-            index = coord.to_index()
-            if not isinstance(index, pd.MultiIndex):
-                raise ValueError("coordinate %r has no MultiIndex" % dim)
-            replace_variables[dim] = IndexVariable(coord.dims,
-                                                   index.reorder_levels(order))
+            replace_variables[dim] = coord.reorder_levels(dim, order)
         variables = self._variables.copy()
         variables.update(replace_variables)
         return self._replace_vars_and_dims(variables, inplace=inplace)
@@ -1790,7 +1794,7 @@ def _stack_once(self, dims, new_dim):
                     variables[name] = stacked_var
                 else:
                     variables[name] = var.copy(deep=False)
-
+        # TODO move to IndexVariable method
         # consider dropping levels that are unused?
         levels = [self.get_index(dim) for dim in dims]
         if hasattr(pd, 'RangeIndex'):

xarray/core/formatting.py

@@ -214,18 +214,25 @@ def _summarize_var_or_coord(name, var, col_width, show_values=True,
     return front_str + values_str
 
 
-def _summarize_coord_multiindex(coord, col_width, marker):
-    first_col = pretty_print(u'  %s %s ' % (marker, coord.name), col_width)
-    return u'%s(%s) MultiIndex' % (first_col, unicode_type(coord.dims[0]))
+def _summarize_coord_multiindex(coord, col_width, marker, name=None):
+    name = name or coord.name
+    first_col = pretty_print(u'  %s %s ' % (marker, name), col_width)
+    if len(coord.dims) == 0:
+        return u'%sMultiIndex' % (first_col)
+    else:
+        return u'%s(%s) MultiIndex' % (first_col, unicode_type(coord.dims[0]))
 
 
 def _summarize_coord_levels(coord, col_width, marker=u'-'):
-    relevant_coord = coord[:30]
+    if len(coord.dims) == 0:
+        relevant_coord = coord  # scalar MultiIndex
+    else:
+        relevant_coord = coord[:30]
     return u'\n'.join(
         [_summarize_var_or_coord(lname,
                                  relevant_coord.get_level_variable(lname),
                                  col_width, marker=marker)
-         for lname in coord.level_names])
+         for lname in coord.all_level_names])
 
 
 def _not_remote(var):
@@ -247,11 +254,11 @@ def summarize_coord(name, var, col_width):
     is_index = name in var.dims
     show_values = is_index or _not_remote(var)
     marker = u'*' if is_index else u' '
-    if is_index:
-        coord = var.variable.to_index_variable()
+    if name in var.coords:
+        coord = var.variable
         if coord.level_names is not None:
             return u'\n'.join(
-                [_summarize_coord_multiindex(coord, col_width, marker),
+                [_summarize_coord_multiindex(coord, col_width, marker, name),
                  _summarize_coord_levels(coord, col_width)])
     return _summarize_var_or_coord(name, var, col_width, show_values, marker)