Preserve Series name in duplicated method. (#16655)

Closes #16654.

Authors:
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - GALI PREM SAGAR (https://github.com/galipremsagar)
  - Matthew Roeschke (https://github.com/mroeschke)

URL: #16655

python/cudf/cudf/core/indexed_frame.py

@@ -3198,8 +3198,10 @@ def duplicated(self, subset=None, keep="first"):
         """
         subset = self._preprocess_subset(subset)
 
+        name = None
         if isinstance(self, cudf.Series):
             columns = [self._column]
+            name = self.name
         else:
             columns = [self._data[n] for n in subset]
         distinct = libcudf.stream_compaction.distinct_indices(
@@ -3211,7 +3213,7 @@ def duplicated(self, subset=None, keep="first"):
             [as_column(True, length=len(self), dtype=bool)],
             bounds_check=False,
         )[0]
-        return cudf.Series._from_column(result, index=self.index)
+        return cudf.Series._from_column(result, index=self.index, name=name)
 
     @_performance_tracking
     def _empty_like(self, keep_index=True) -> Self:

python/cudf/cudf/tests/test_series.py

@@ -2115,8 +2115,9 @@ def test_series_hasnans(data):
     ],
 )
 @pytest.mark.parametrize("keep", ["first", "last", False])
-def test_series_duplicated(data, index, keep):
-    gs = cudf.Series(data, index=index)
+@pytest.mark.parametrize("name", [None, "a"])
+def test_series_duplicated(data, index, keep, name):
+    gs = cudf.Series(data, index=index, name=name)
     ps = gs.to_pandas()
 
     assert_eq(gs.duplicated(keep=keep), ps.duplicated(keep=keep))