BUG: Fix #61222: Keep index name when resampling with pyarrow dtype

Author: mthiboust

doc/source/whatsnew/v3.0.0.rst

@@ -784,6 +784,7 @@ Groupby/resample/rolling
 - Bug in :meth:`Rolling.apply` for ``method="table"`` where column order was not being respected due to the columns getting sorted by default. (:issue:`59666`)
 - Bug in :meth:`Rolling.apply` where the applied function could be called on fewer than ``min_period`` periods if ``method="table"``. (:issue:`58868`)
 - Bug in :meth:`Series.resample` could raise when the the date range ended shortly before a non-existent time. (:issue:`58380`)
+- Bug in :meth:`DataFrame.resample` and `Series.resample` were not keeping the index name when the index had :class:`pyarrow` datetime dtype (:issue:`61222`)
 
 Reshaping
 ^^^^^^^^^

pandas/core/resample.py

@@ -518,6 +518,7 @@ def _wrap_result(self, result):
 
         if self._timegrouper._arrow_dtype is not None:
             result.index = result.index.astype(self._timegrouper._arrow_dtype)
+            result.index.name = self.obj.index.name
 
         return result
 

pandas/tests/resample/test_datetime_index.py

@@ -2155,6 +2155,16 @@ def test_arrow_timestamp_resample(tz):
     tm.assert_series_equal(result, expected)
 
 
+@td.skip_if_no("pyarrow")
+def test_arrow_timestamp_resample_keep_index_name():
+    # https://github.com/pandas-dev/pandas/issues/61222
+    idx = Series(date_range("2020-01-01", periods=5), dtype="timestamp[ns][pyarrow]")
+    expected = Series(np.arange(5, dtype=np.float64), index=idx)
+    expected.index.name = "index_name"
+    result = expected.resample("1D").mean()
+    tm.assert_series_equal(result, expected) 
+
+
 @pytest.mark.parametrize("freq", ["1A", "2A-MAR"])
 def test_resample_A_raises(freq):
     msg = f"Invalid frequency: {freq[1:]}"