More explicit index handling in dataset.py

xarray/core/dataset.py

@@ -21,9 +21,12 @@
 from .coordinates import (DatasetCoordinates, LevelCoordinatesSource,
                           assert_coordinate_consistent, remap_label_indexers)
 from .duck_array_ops import datetime_to_numeric
-from .indexes import Indexes, default_indexes, isel_variable_and_index
-from .merge import (dataset_merge_method, dataset_update_method,
-                    merge_data_and_coords, merge_variables)
+from .indexes import (
+    Indexes, default_indexes, isel_variable_and_index, roll_index,
+)
+from .merge import (
+    dataset_merge_method, dataset_update_method, merge_data_and_coords,
+    merge_variables)
 from .options import OPTIONS, _get_keep_attrs
 from .pycompat import TYPE_CHECKING, dask_array_type
 from .utils import (Frozen, SortedKeysDict, _check_inplace,
@@ -2693,17 +2696,18 @@ def reorder_levels(self, dim_order=None, inplace=None,
         inplace = _check_inplace(inplace)
         dim_order = either_dict_or_kwargs(dim_order, dim_order_kwargs,
                                           'reorder_levels')
-        replace_variables = {}
+        variables = self._variables.copy()
+        indexes = OrderedDict(self.indexes)
         for dim, order in dim_order.items():
             coord = self._variables[dim]
-            index = coord.to_index()
+            index = self.indexes[dim]
             if not isinstance(index, pd.MultiIndex):
                 raise ValueError("coordinate %r has no MultiIndex" % dim)
-            replace_variables[dim] = IndexVariable(coord.dims,
-                                                   index.reorder_levels(order))
-        variables = self._variables.copy()
-        variables.update(replace_variables)
-        return self._replace_vars_and_dims(variables, inplace=inplace)
+            new_index = index.reorder_levels(order)
+            variables[dim] = IndexVariable(coord.dims, new_index)
+            indexes[dim] = new_index
+
+        return self._replace(variables, indexes=indexes, inplace=inplace)
 
     def _stack_once(self, dims, new_dim):
         variables = OrderedDict()
@@ -2733,7 +2737,12 @@ def _stack_once(self, dims, new_dim):
 
         coord_names = set(self._coord_names) - set(dims) | set([new_dim])
 
-        return self._replace_vars_and_dims(variables, coord_names)
+        indexes = OrderedDict((k, v) for k, v in self.indexes.items()
+                              if k not in dims)
+        indexes[new_dim] = idx
+
+        return self._replace_with_new_dims(
+            variables, coord_names=coord_names, indexes=indexes)
 
     def stack(self, dimensions=None, **dimensions_kwargs):
         """
@@ -2900,6 +2909,9 @@ def _unstack_once(self, dim):
         new_dim_sizes = [lev.size for lev in index.levels]
 
         variables = OrderedDict()
+        indexes = OrderedDict(
+            (k, v) for k, v in self.indexes.items() if k != dim)
+
         for name, var in obj.variables.items():
             if name != dim:
                 if dim in var.dims:
@@ -2910,10 +2922,12 @@ def _unstack_once(self, dim):
 
         for name, lev in zip(new_dim_names, index.levels):
             variables[name] = IndexVariable(name, lev)
+            indexes[name] = lev
 
         coord_names = set(self._coord_names) - set([dim]) | set(new_dim_names)
 
-        return self._replace_vars_and_dims(variables, coord_names)
+        return self._replace_with_new_dims(
+            variables, coord_names=coord_names, indexes=indexes)
 
     def unstack(self, dim=None):
         """
@@ -3098,7 +3112,10 @@ def _drop_vars(self, names, errors='raise'):
         variables = OrderedDict((k, v) for k, v in self._variables.items()
                                 if k not in drop)
         coord_names = set(k for k in self._coord_names if k in variables)
-        return self._replace_vars_and_dims(variables, coord_names)
+        indexes = OrderedDict((k, v) for k, v in self.indexes.items()
+                              if k not in drop)
+        return self._replace_with_new_dims(
+            variables, coord_names=coord_names, indexes=indexes)
 
     def drop_dims(self, drop_dims, *, errors='raise'):
         """Drop dimensions and associated variables from this dataset.
@@ -3133,12 +3150,7 @@ def drop_dims(self, drop_dims, *, errors='raise'):
 
         drop_vars = set(k for k, v in self._variables.items()
                         for d in v.dims if d in drop_dims)
-
-        variables = OrderedDict((k, v) for k, v in self._variables.items()
-                                if k not in drop_vars)
-        coord_names = set(k for k in self._coord_names if k in variables)
-
-        return self._replace_with_new_dims(variables, coord_names)
+        return self._drop_vars(drop_vars)
 
     def transpose(self, *dims):
         """Return a new Dataset object with all array dimensions transposed.
@@ -3457,8 +3469,11 @@ def reduce(self, func, dim=None, keep_attrs=None, keepdims=False,
                                                  **kwargs)
 
         coord_names = set(k for k in self.coords if k in variables)
+        indexes = OrderedDict((k, v) for k, v in self.indexes.items()
+                              if k in variables)
         attrs = self.attrs if keep_attrs else None
-        return self._replace_vars_and_dims(variables, coord_names, attrs=attrs)
+        return self._replace_with_new_dims(
+            variables, coord_names=coord_names, attrs=attrs, indexes=indexes)
 
     def apply(self, func, keep_attrs=None, args=(), **kwargs):
         """Apply a function over the data variables in this dataset.
@@ -3854,8 +3869,9 @@ def func(self, other):
                 other = other.reindex_like(self, copy=False)
             g = ops.inplace_to_noninplace_op(f)
             ds = self._calculate_binary_op(g, other, inplace=True)
-            self._replace_vars_and_dims(ds._variables, ds._coord_names,
-                                        attrs=ds._attrs, inplace=True)
+            self._replace_with_new_dims(ds._variables, ds._coord_names,
+                                        attrs=ds._attrs, indexes=ds._indexes,
+                                        inplace=True)
             return self
 
         return func
@@ -3980,7 +3996,11 @@ def diff(self, dim, n=1, label='upper'):
             else:
                 variables[name] = var
 
-        difference = self._replace_vars_and_dims(variables)
+        indexes = OrderedDict(self.indexes)
+        if dim in indexes:
+            indexes[dim] = indexes[dim][kwargs_new[dim]]
+
+        difference = self._replace_with_new_dims(variables, indexes=indexes)
 
         if n > 1:
             return difference.diff(dim, n - 1)
@@ -4042,7 +4062,7 @@ def shift(self, shifts=None, fill_value=dtypes.NA, **shifts_kwargs):
             else:
                 variables[name] = var
 
-        return self._replace_vars_and_dims(variables)
+        return self._replace(variables)
 
     def roll(self, shifts=None, roll_coords=None, **shifts_kwargs):
         """Roll this dataset by an offset along one or more dimensions.
@@ -4109,7 +4129,16 @@ def roll(self, shifts=None, roll_coords=None, **shifts_kwargs):
             else:
                 variables[k] = v
 
-        return self._replace_vars_and_dims(variables)
+        if roll_coords:
+            indexes = OrderedDict()
+            for k, v in self.indexes.items():
+                (dim,) = self.variables[k].dims
+                if dim in shifts:
+                    indexes[k] = roll_index(v, shifts[dim])
+        else:
+            indexes = OrderedDict(self.indexes)
+
+        return self._replace(variables, indexes=indexes)
 
     def sortby(self, variables, ascending=True):
         """
@@ -4251,10 +4280,14 @@ def quantile(self, q, dim=None, interpolation='linear',
 
         # construct the new dataset
         coord_names = set(k for k in self.coords if k in variables)
+        indexes = OrderedDict(
+            (k, v) for k, v in self.indexes.items() if k in variables
+        )
         if keep_attrs is None:
             keep_attrs = _get_keep_attrs(default=False)
         attrs = self.attrs if keep_attrs else None
-        new = self._replace_vars_and_dims(variables, coord_names, attrs=attrs)
+        new = self._replace_with_new_dims(
+            variables, coord_names=coord_names, attrs=attrs, indexes=indexes)
         if 'quantile' in new.dims:
             new.coords['quantile'] = Variable('quantile', q)
         else:
@@ -4305,7 +4338,7 @@ def rank(self, dim, pct=False, keep_attrs=None):
         if keep_attrs is None:
             keep_attrs = _get_keep_attrs(default=False)
         attrs = self.attrs if keep_attrs else None
-        return self._replace_vars_and_dims(variables, coord_names, attrs=attrs)
+        return self._replace(variables, coord_names, attrs=attrs)
 
     def differentiate(self, coord, edge_order=1, datetime_unit=None):
         """ Differentiate with the second order accurate central
@@ -4363,7 +4396,7 @@ def differentiate(self, coord, edge_order=1, datetime_unit=None):
                 variables[k] = Variable(v.dims, grad)
             else:
                 variables[k] = v
-        return self._replace_vars_and_dims(variables)
+        return self._replace(variables)
 
     def integrate(self, coord, datetime_unit=None):
         """ integrate the array with the trapezoidal rule.
@@ -4435,7 +4468,11 @@ def _integrate_one(self, coord, datetime_unit=None):
                     variables[k] = Variable(v_dims, integ)
                 else:
                     variables[k] = v
-        return self._replace_vars_and_dims(variables, coord_names=coord_names)
+        indexes = OrderedDict(
+            (k, v) for k, v in self.indexes.items() if k in variables
+        )
+        return self._replace_with_new_dims(
+            variables, coord_names=coord_names, indexes=indexes)
 
     @property
     def real(self):

xarray/core/indexes.py

@@ -87,3 +87,12 @@ def isel_variable_and_index(
         indexer = indexer.data
     new_index = index[indexer]
     return new_variable, new_index
+
+
+def roll_index(index: pd.Index, count: int, axis: int = 0) -> pd.Index:
+    """Roll an pandas.Index."""
+    count %= index.shape[0]
+    if count != 0:
+        return index[-count:].append(index[:-count])
+    else:
+        return index[:]