Refactor Grouper objects (#8776)

* Refactor resampling.

1. Rename to Resampler from ResampleGrouper
2. Move code from common.resample to TimeResampler

* Single Grouper class

* Fixes

* Fixes

* Add comments.

* Apply suggestions from code review

Co-authored-by: Illviljan <[email protected]>

* Review feedback

* fix

---------

Co-authored-by: Illviljan <[email protected]>

Author: dcherian

xarray/core/common.py

@@ -16,7 +16,6 @@
 from xarray.core.utils import (
     Frozen,
     either_dict_or_kwargs,
-    emit_user_level_warning,
     is_scalar,
 )
 from xarray.namedarray.core import _raise_if_any_duplicate_dimensions
@@ -1050,8 +1049,7 @@ def _resample(
         # TODO support non-string indexer after removing the old API.
 
         from xarray.core.dataarray import DataArray
-        from xarray.core.groupby import ResolvedTimeResampleGrouper, TimeResampleGrouper
-        from xarray.core.pdcompat import _convert_base_to_offset
+        from xarray.core.groupby import ResolvedGrouper, TimeResampler
         from xarray.core.resample import RESAMPLE_DIM
 
         # note: the second argument (now 'skipna') use to be 'dim'
@@ -1074,44 +1072,24 @@ def _resample(
         dim_name: Hashable = dim
         dim_coord = self[dim]
 
-        if loffset is not None:
-            emit_user_level_warning(
-                "Following pandas, the `loffset` parameter to resample is deprecated.  "
-                "Switch to updating the resampled dataset time coordinate using "
-                "time offset arithmetic.  For example:\n"
-                "    >>> offset = pd.tseries.frequencies.to_offset(freq) / 2\n"
-                '    >>> resampled_ds["time"] = resampled_ds.get_index("time") + offset',
-                FutureWarning,
-            )
-
-        if base is not None:
-            emit_user_level_warning(
-                "Following pandas, the `base` parameter to resample will be deprecated in "
-                "a future version of xarray.  Switch to using `origin` or `offset` instead.",
-                FutureWarning,
-            )
-
-        if base is not None and offset is not None:
-            raise ValueError("base and offset cannot be present at the same time")
-
-        if base is not None:
-            index = self._indexes[dim_name].to_pandas_index()
-            offset = _convert_base_to_offset(base, freq, index)
+        group = DataArray(
+            dim_coord,
+            coords=dim_coord.coords,
+            dims=dim_coord.dims,
+            name=RESAMPLE_DIM,
+        )
 
-        grouper = TimeResampleGrouper(
+        grouper = TimeResampler(
             freq=freq,
             closed=closed,
             label=label,
             origin=origin,
             offset=offset,
             loffset=loffset,
+            base=base,
         )
 
-        group = DataArray(
-            dim_coord, coords=dim_coord.coords, dims=dim_coord.dims, name=RESAMPLE_DIM
-        )
-
-        rgrouper = ResolvedTimeResampleGrouper(grouper, group, self)
+        rgrouper = ResolvedGrouper(grouper, group, self)
 
         return resample_cls(
             self,

xarray/core/dataarray.py

@@ -6704,13 +6704,13 @@ def groupby(
         """
         from xarray.core.groupby import (
             DataArrayGroupBy,
-            ResolvedUniqueGrouper,
+            ResolvedGrouper,
             UniqueGrouper,
             _validate_groupby_squeeze,
         )
 
         _validate_groupby_squeeze(squeeze)
-        rgrouper = ResolvedUniqueGrouper(UniqueGrouper(), group, self)
+        rgrouper = ResolvedGrouper(UniqueGrouper(), group, self)
         return DataArrayGroupBy(
             self,
             (rgrouper,),
@@ -6789,7 +6789,7 @@ def groupby_bins(
         from xarray.core.groupby import (
             BinGrouper,
             DataArrayGroupBy,
-            ResolvedBinGrouper,
+            ResolvedGrouper,
             _validate_groupby_squeeze,
         )
 
@@ -6803,7 +6803,7 @@ def groupby_bins(
                 "include_lowest": include_lowest,
             },
         )
-        rgrouper = ResolvedBinGrouper(grouper, group, self)
+        rgrouper = ResolvedGrouper(grouper, group, self)
 
         return DataArrayGroupBy(
             self,

xarray/core/dataset.py

@@ -10179,13 +10179,13 @@ def groupby(
         """
         from xarray.core.groupby import (
             DatasetGroupBy,
-            ResolvedUniqueGrouper,
+            ResolvedGrouper,
             UniqueGrouper,
             _validate_groupby_squeeze,
         )
 
         _validate_groupby_squeeze(squeeze)
-        rgrouper = ResolvedUniqueGrouper(UniqueGrouper(), group, self)
+        rgrouper = ResolvedGrouper(UniqueGrouper(), group, self)
 
         return DatasetGroupBy(
             self,
@@ -10265,7 +10265,7 @@ def groupby_bins(
         from xarray.core.groupby import (
             BinGrouper,
             DatasetGroupBy,
-            ResolvedBinGrouper,
+            ResolvedGrouper,
             _validate_groupby_squeeze,
         )
 
@@ -10279,7 +10279,7 @@ def groupby_bins(
                 "include_lowest": include_lowest,
             },
         )
-        rgrouper = ResolvedBinGrouper(grouper, group, self)
+        rgrouper = ResolvedGrouper(grouper, group, self)
 
         return DatasetGroupBy(
             self,