ExtensionArray.Round method and tests

doc/source/whatsnew/v3.0.0.rst

@@ -360,7 +360,7 @@ Sparse
 ExtensionArray
 ^^^^^^^^^^^^^^
 - Fixed bug in :meth:`api.types.is_datetime64_any_dtype` where a custom :class:`ExtensionDtype` would return ``False`` for array-likes (:issue:`57055`)
--
+- A default, unoptimised :meth:`ExtensionArray.round` method is now provided for numeric ExtensionArrays (:issue:`49387`)
 
 Styler
 ^^^^^^

pandas/core/arrays/arrow/array.py

@@ -1212,7 +1212,10 @@ def round(self, decimals: int = 0, *args, **kwargs) -> Self:
         DataFrame.round : Round values of a DataFrame.
         Series.round : Round values of a Series.
         """
-        return type(self)(pc.round(self._pa_array, ndigits=decimals))
+        if not self.dtype._is_numeric or self.dtype._is_boolean:
+            raise TypeError("Cannot round non-numeric type.")
+        result = pc.round(self._pa_array, ndigits=decimals)
+        return type(self)(result.cast(self._pa_array.type))
 
     @doc(ExtensionArray.searchsorted)
     def searchsorted(

pandas/core/arrays/base.py

@@ -2278,6 +2278,22 @@ def _mode(self, dropna: bool = True) -> Self:
         # ndarray[Any, Any]]", expected "Self")
         return mode(self, dropna=dropna)  # type: ignore[return-value]
 
+    def round(self, decimals: int = 0, *args, **kwargs) -> Self:
+        # Implementer note: This is a non-optimized default implementation.
+        # Implementers are encouraged to override this method to avoid
+        # elementwise rounding.
+        if self.dtype._is_boolean:
+            return self
+        if not self.dtype._is_numeric:
+            raise TypeError(f"Cannot round {type(self)} dtype as it is non-numeric")
+        return self._from_sequence(
+            [
+                round(element) if not element_isna else element
+                for (element, element_isna) in zip(self, self.isna())
+            ],
+            dtype=self.dtype,
+        )
+
     def __array_ufunc__(self, ufunc: np.ufunc, method: str, *inputs, **kwargs):
         if any(
             isinstance(other, (ABCSeries, ABCIndex, ABCDataFrame)) for other in inputs

pandas/core/arrays/datetimelike.py

@@ -2285,7 +2285,7 @@ def _round(self, freq, mode, ambiguous, nonexistent):
         return self._simple_new(result, dtype=self.dtype)
 
     @Appender((_round_doc + _round_example).format(op="round"))
-    def round(
+    def round(  # type: ignore[override]
         self,
         freq,
         ambiguous: TimeAmbiguous = "raise",

pandas/core/arrays/sparse/array.py

@@ -1671,6 +1671,15 @@ def argmin(self, skipna: bool = True) -> int:
             raise NotImplementedError
         return self._argmin_argmax("argmin")
 
+    def round(self, decimals: int = 0, *args, **kwargs) -> Self:
+        new_values = np.array(
+            [
+                round(element) if not isna(element) else element
+                for element in self.sp_values
+            ]
+        )
+        return self._simple_new(new_values, self._sparse_index, self.dtype)
+
     # ------------------------------------------------------------------------
     # Ufuncs
     # ------------------------------------------------------------------------

pandas/core/internals/blocks.py

@@ -1523,11 +1523,7 @@ def round(self, decimals: int) -> Self:
         """
         if not self.is_numeric or self.is_bool:
             return self.copy(deep=False)
-        # TODO: round only defined on BaseMaskedArray
-        # Series also does this, so would need to fix both places
-        # error: Item "ExtensionArray" of "Union[ndarray[Any, Any], ExtensionArray]"
-        # has no attribute "round"
-        values = self.values.round(decimals)  # type: ignore[union-attr]
+        values = self.values.round(decimals)
 
         refs = None
         if values is self.values:

pandas/tests/extension/base/methods.py

@@ -718,3 +718,19 @@ def test_equals(self, data, na_value, as_series, box):
     def test_equals_same_data_different_object(self, data):
         # https://github.com/pandas-dev/pandas/issues/34660
         assert pd.Series(data).equals(pd.Series(data))
+
+    def test_round(self, data):
+        if not data.dtype._is_numeric:
+            with pytest.raises(TypeError):
+                data.round()
+        elif data.dtype._is_boolean:
+            result = pd.Series(data).round()
+            expected = pd.Series(data)
+            tm.assert_series_equal(result, expected)
+        else:
+            result = pd.Series(data).round()
+            expected = pd.Series(
+                [round(element) if pd.notna(element) else element for element in data],
+                dtype=data.dtype,
+            )
+            tm.assert_series_equal(result, expected)

pandas/tests/extension/test_datetime.py

@@ -139,6 +139,10 @@ def check_reduce(self, ser: pd.Series, op_name: str, skipna: bool):
         else:
             return super().check_reduce(ser, op_name, skipna)
 
+    @pytest.mark.skip("DatetimeArray uses a different function signature for round")
+    def test_round(self):
+        pass
+
 
 class Test2DCompat(base.NDArrayBacked2DTests):
     pass