BUG: Preserve name in Index.astype

doc/source/whatsnew/v1.1.0.rst

@@ -376,6 +376,7 @@ Reshaping
 - Bug in :func:`crosstab` when inputs are two Series and have tuple names, the output will keep dummy MultiIndex as columns. (:issue:`18321`)
 - :meth:`DataFrame.pivot` can now take lists for ``index`` and ``columns`` arguments (:issue:`21425`)
 - Bug in :func:`concat` where the resulting indices are not copied when ``copy=True`` (:issue:`29879`)
+- Bug where :meth:`Index.astype` would lose the name attribute when converting from ``Float64Index`` to ``Int64Index``, or when casting to an ``ExtensionArray`` dtype (:issue:`32013`)
 - :meth:`Series.append` will now raise a ``TypeError`` when passed a DataFrame or a sequence containing Dataframe (:issue:`31413`)
 - :meth:`DataFrame.replace` and :meth:`Series.replace` will raise a ``TypeError`` if ``to_replace`` is not an expected type. Previously the ``replace`` would fail silently (:issue:`18634`)
 - Bug in :meth:`DataFrame.apply` where callback was called with :class:`Series` parameter even though ``raw=True`` requested. (:issue:`32423`)

pandas/core/indexes/base.py

@@ -670,7 +670,7 @@ def astype(self, dtype, copy=True):
             return CategoricalIndex(self.values, name=self.name, dtype=dtype, copy=copy)
 
         elif is_extension_array_dtype(dtype):
-            return Index(np.asarray(self), dtype=dtype, copy=copy)
+            return Index(np.asarray(self), name=self.name, dtype=dtype, copy=copy)
 
         try:
             casted = self.values.astype(dtype, copy=copy)

pandas/core/indexes/numeric.py

@@ -369,7 +369,7 @@ def astype(self, dtype, copy=True):
             # TODO(jreback); this can change once we have an EA Index type
             # GH 13149
             arr = astype_nansafe(self._values, dtype=dtype)
-            return Int64Index(arr)
+            return Int64Index(arr, name=self.name)
         return super().astype(dtype, copy=copy)
 
     # ----------------------------------------------------------------

pandas/tests/indexes/datetimes/test_astype.py

@@ -22,27 +22,32 @@
 class TestDatetimeIndex:
     def test_astype(self):
         # GH 13149, GH 13209
-        idx = DatetimeIndex(["2016-05-16", "NaT", NaT, np.NaN])
+        idx = DatetimeIndex(["2016-05-16", "NaT", NaT, np.NaN], name="idx")
 
         result = idx.astype(object)
-        expected = Index([Timestamp("2016-05-16")] + [NaT] * 3, dtype=object)
+        expected = Index(
+            [Timestamp("2016-05-16")] + [NaT] * 3, dtype=object, name="idx"
+        )
         tm.assert_index_equal(result, expected)
 
         result = idx.astype(int)
         expected = Int64Index(
-            [1463356800000000000] + [-9223372036854775808] * 3, dtype=np.int64
+            [1463356800000000000] + [-9223372036854775808] * 3,
+            dtype=np.int64,
+            name="idx",
         )
         tm.assert_index_equal(result, expected)
 
-        rng = date_range("1/1/2000", periods=10)
+        rng = date_range("1/1/2000", periods=10, name="idx")
         result = rng.astype("i8")
-        tm.assert_index_equal(result, Index(rng.asi8))
+        tm.assert_index_equal(result, Index(rng.asi8, name="idx"))
         tm.assert_numpy_array_equal(result.values, rng.asi8)
 
     def test_astype_uint(self):
-        arr = date_range("2000", periods=2)
+        arr = date_range("2000", periods=2, name="idx")
         expected = pd.UInt64Index(
-            np.array([946684800000000000, 946771200000000000], dtype="uint64")
+            np.array([946684800000000000, 946771200000000000], dtype="uint64"),
+            name="idx",
         )
 
         tm.assert_index_equal(arr.astype("uint64"), expected)
@@ -148,7 +153,7 @@ def test_astype_str(self):
 
     def test_astype_datetime64(self):
         # GH 13149, GH 13209
-        idx = DatetimeIndex(["2016-05-16", "NaT", NaT, np.NaN])
+        idx = DatetimeIndex(["2016-05-16", "NaT", NaT, np.NaN], name="idx")
 
         result = idx.astype("datetime64[ns]")
         tm.assert_index_equal(result, idx)
@@ -158,10 +163,12 @@ def test_astype_datetime64(self):
         tm.assert_index_equal(result, idx)
         assert result is idx
 
-        idx_tz = DatetimeIndex(["2016-05-16", "NaT", NaT, np.NaN], tz="EST")
+        idx_tz = DatetimeIndex(["2016-05-16", "NaT", NaT, np.NaN], tz="EST", name="idx")
         result = idx_tz.astype("datetime64[ns]")
         expected = DatetimeIndex(
-            ["2016-05-16 05:00:00", "NaT", "NaT", "NaT"], dtype="datetime64[ns]"
+            ["2016-05-16 05:00:00", "NaT", "NaT", "NaT"],
+            dtype="datetime64[ns]",
+            name="idx",
         )
         tm.assert_index_equal(result, expected)
 
@@ -273,8 +280,8 @@ def _check_rng(rng):
     def test_integer_index_astype_datetime(self, tz, dtype):
         # GH 20997, 20964, 24559
         val = [pd.Timestamp("2018-01-01", tz=tz).value]
-        result = pd.Index(val).astype(dtype)
-        expected = pd.DatetimeIndex(["2018-01-01"], tz=tz)
+        result = pd.Index(val, name="idx").astype(dtype)
+        expected = pd.DatetimeIndex(["2018-01-01"], tz=tz, name="idx")
         tm.assert_index_equal(result, expected)
 
     def test_dti_astype_period(self):
@@ -292,10 +299,11 @@ def test_dti_astype_period(self):
 class TestAstype:
     @pytest.mark.parametrize("tz", [None, "US/Central"])
     def test_astype_category(self, tz):
-        obj = pd.date_range("2000", periods=2, tz=tz)
+        obj = pd.date_range("2000", periods=2, tz=tz, name="idx")
         result = obj.astype("category")
         expected = pd.CategoricalIndex(
-            [pd.Timestamp("2000-01-01", tz=tz), pd.Timestamp("2000-01-02", tz=tz)]
+            [pd.Timestamp("2000-01-01", tz=tz), pd.Timestamp("2000-01-02", tz=tz)],
+            name="idx",
         )
         tm.assert_index_equal(result, expected)
 
@@ -305,9 +313,9 @@ def test_astype_category(self, tz):
 
     @pytest.mark.parametrize("tz", [None, "US/Central"])
     def test_astype_array_fallback(self, tz):
-        obj = pd.date_range("2000", periods=2, tz=tz)
+        obj = pd.date_range("2000", periods=2, tz=tz, name="idx")
         result = obj.astype(bool)
-        expected = pd.Index(np.array([True, True]))
+        expected = pd.Index(np.array([True, True]), name="idx")
         tm.assert_index_equal(result, expected)
 
         result = obj._data.astype(bool)

pandas/tests/indexes/period/test_astype.py

@@ -27,31 +27,34 @@ def test_astype_raises(self, dtype):
 
     def test_astype_conversion(self):
         # GH#13149, GH#13209
-        idx = PeriodIndex(["2016-05-16", "NaT", NaT, np.NaN], freq="D")
+        idx = PeriodIndex(["2016-05-16", "NaT", NaT, np.NaN], freq="D", name="idx")
 
         result = idx.astype(object)
         expected = Index(
             [Period("2016-05-16", freq="D")] + [Period(NaT, freq="D")] * 3,
             dtype="object",
+            name="idx",
         )
         tm.assert_index_equal(result, expected)
 
         result = idx.astype(np.int64)
-        expected = Int64Index([16937] + [-9223372036854775808] * 3, dtype=np.int64)
+        expected = Int64Index(
+            [16937] + [-9223372036854775808] * 3, dtype=np.int64, name="idx"
+        )
         tm.assert_index_equal(result, expected)
 
         result = idx.astype(str)
-        expected = Index(str(x) for x in idx)
+        expected = Index([str(x) for x in idx], name="idx")
         tm.assert_index_equal(result, expected)
 
-        idx = period_range("1990", "2009", freq="A")
+        idx = period_range("1990", "2009", freq="A", name="idx")
         result = idx.astype("i8")
-        tm.assert_index_equal(result, Index(idx.asi8))
+        tm.assert_index_equal(result, Index(idx.asi8, name="idx"))
         tm.assert_numpy_array_equal(result.values, idx.asi8)
 
     def test_astype_uint(self):
-        arr = period_range("2000", periods=2)
-        expected = UInt64Index(np.array([10957, 10958], dtype="uint64"))
+        arr = period_range("2000", periods=2, name="idx")
+        expected = UInt64Index(np.array([10957, 10958], dtype="uint64"), name="idx")
         tm.assert_index_equal(arr.astype("uint64"), expected)
         tm.assert_index_equal(arr.astype("uint32"), expected)
 
@@ -116,10 +119,10 @@ def test_astype_object2(self):
         assert result_list[2] is NaT
 
     def test_astype_category(self):
-        obj = period_range("2000", periods=2)
+        obj = period_range("2000", periods=2, name="idx")
         result = obj.astype("category")
         expected = CategoricalIndex(
-            [Period("2000-01-01", freq="D"), Period("2000-01-02", freq="D")]
+            [Period("2000-01-01", freq="D"), Period("2000-01-02", freq="D")], name="idx"
         )
         tm.assert_index_equal(result, expected)
 
@@ -128,9 +131,9 @@ def test_astype_category(self):
         tm.assert_categorical_equal(result, expected)
 
     def test_astype_array_fallback(self):
-        obj = period_range("2000", periods=2)
+        obj = period_range("2000", periods=2, name="idx")
         result = obj.astype(bool)
-        expected = Index(np.array([True, True]))
+        expected = Index(np.array([True, True]), name="idx")
         tm.assert_index_equal(result, expected)
 
         result = obj._data.astype(bool)

pandas/tests/indexes/test_common.py

@@ -373,3 +373,29 @@ def test_has_duplicates(self, indices):
         idx = holder([indices[0]] * 5)
         assert idx.is_unique is False
         assert idx.has_duplicates is True
+
+    @pytest.mark.parametrize(
+        "dtype",
+        ["int64", "uint64", "float64", "category", "datetime64[ns]", "timedelta64[ns]"],
+    )
+    @pytest.mark.parametrize("copy", [True, False])
+    def test_astype_preserves_name(self, indices, dtype, copy):
+        # https://github.com/pandas-dev/pandas/issues/32013
+        if isinstance(indices, MultiIndex):
+            indices.names = ["idx1", "idx2"]
+        else:
+            indices.name = "idx"
+
+        try:
+            # Some of these conversions cannot succeed so we use a try / except
+            if copy:
+                result = indices.copy(dtype=dtype)
+            else:
+                result = indices.astype(dtype)
+        except (ValueError, TypeError, NotImplementedError, SystemError):
+            return
+
+        if isinstance(indices, MultiIndex):
+            assert result.names == indices.names
+        else:
+            assert result.name == indices.name

pandas/tests/indexes/timedeltas/test_astype.py

@@ -47,20 +47,22 @@ def test_astype_object_with_nat(self):
 
     def test_astype(self):
         # GH 13149, GH 13209
-        idx = TimedeltaIndex([1e14, "NaT", NaT, np.NaN])
+        idx = TimedeltaIndex([1e14, "NaT", NaT, np.NaN], name="idx")
 
         result = idx.astype(object)
-        expected = Index([Timedelta("1 days 03:46:40")] + [NaT] * 3, dtype=object)
+        expected = Index(
+            [Timedelta("1 days 03:46:40")] + [NaT] * 3, dtype=object, name="idx"
+        )
         tm.assert_index_equal(result, expected)
 
         result = idx.astype(int)
         expected = Int64Index(
-            [100000000000000] + [-9223372036854775808] * 3, dtype=np.int64
+            [100000000000000] + [-9223372036854775808] * 3, dtype=np.int64, name="idx"
         )
         tm.assert_index_equal(result, expected)
 
         result = idx.astype(str)
-        expected = Index(str(x) for x in idx)
+        expected = Index([str(x) for x in idx], name="idx")
         tm.assert_index_equal(result, expected)
 
         rng = timedelta_range("1 days", periods=10)