PERF: Series.fillna for pyarrow-backed dtypes

asv_bench/benchmarks/series_methods.py

@@ -79,6 +79,48 @@ def time_dropna(self, dtype):
         self.s.dropna()
 
 
+class Fillna:
+
+    params = [
+        [
+            "datetime64[ns]",
+            "float64",
+            "Int64",
+            "int64[pyarrow]",
+            "string",
+            "string[pyarrow]",
+        ],
+        [None, "pad", "backfill"],
+    ]
+    param_names = ["dtype", "method"]
+
+    def setup(self, dtype, method):
+        N = 10**6
+        if dtype == "datetime64[ns]":
+            data = date_range("2000-01-01", freq="S", periods=N)
+            na_value = NaT
+        elif dtype == "float64":
+            data = np.random.randn(N)
+            na_value = np.nan
+        elif dtype in ("Int64", "int64[pyarrow]"):
+            data = np.arange(N)
+            na_value = NA
+        elif dtype in ("string", "string[pyarrow]"):
+            data = tm.rands_array(5, N)
+            na_value = NA
+        else:
+            raise NotImplementedError
+        fill_value = data[0]
+        ser = Series(data, dtype=dtype)
+        ser[::2] = na_value
+        self.ser = ser
+        self.fill_value = fill_value
+
+    def time_fillna(self, dtype, method):
+        value = self.fill_value if method is None else None
+        self.ser.fillna(value=value, method=method)
+
+
 class SearchSorted:
 
     goal_time = 0.2

doc/source/whatsnew/v2.0.0.rst

@@ -573,6 +573,7 @@ Performance improvements
 - Performance improvement in :meth:`.DataFrameGroupBy.mean`, :meth:`.SeriesGroupBy.mean`, :meth:`.DataFrameGroupBy.var`, and :meth:`.SeriesGroupBy.var` for extension array dtypes (:issue:`37493`)
 - Performance improvement in :meth:`MultiIndex.isin` when ``level=None`` (:issue:`48622`, :issue:`49577`)
 - Performance improvement in :meth:`Index.union` and :meth:`MultiIndex.union` when index contains duplicates (:issue:`48900`)
+- Performance improvement in :meth:`Series.fillna` for pyarrow-backed dtypes (:issue:`49722`)
 - Performance improvement for :meth:`Series.value_counts` with nullable dtype (:issue:`48338`)
 - Performance improvement for :class:`Series` constructor passing integer numpy array with nullable dtype (:issue:`48338`)
 - Performance improvement for :class:`DatetimeIndex` constructor passing a list (:issue:`48609`)

pandas/core/arrays/arrow/array.py

@@ -4,12 +4,15 @@
     TYPE_CHECKING,
     Any,
     TypeVar,
+    cast,
 )
 
 import numpy as np
 
 from pandas._typing import (
+    ArrayLike,
     Dtype,
+    FillnaOptions,
     PositionalIndexer,
     SortKind,
     TakeIndexer,
@@ -20,6 +23,7 @@
     pa_version_under7p0,
 )
 from pandas.util._decorators import doc
+from pandas.util._validators import validate_fillna_kwargs
 
 from pandas.core.dtypes.common import (
     is_array_like,
@@ -521,6 +525,66 @@ def dropna(self: ArrowExtensionArrayT) -> ArrowExtensionArrayT:
         else:
             return type(self)(pc.drop_null(self._data))
 
+    @doc(ExtensionArray.fillna)
+    def fillna(
+        self: ArrowExtensionArrayT,
+        value: object | ArrayLike | None = None,
+        method: FillnaOptions | None = None,
+        limit: int | None = None,
+    ) -> ArrowExtensionArrayT:
+
+        value, method = validate_fillna_kwargs(value, method)
+
+        if limit is not None:
+            return super().fillna(value=value, method=method, limit=limit)
+
+        if method is not None and pa_version_under7p0:
+            # fill_null_{forward|backward} added in pyarrow 7.0
+            fallback_performancewarning(version="7")
+            return super().fillna(value=value, method=method, limit=limit)
+
+        if is_array_like(value):
+            value = cast(ArrayLike, value)
+            if len(value) != len(self):
+                raise ValueError(
+                    f"Length of 'value' does not match. Got ({len(value)}) "
+                    f" expected {len(self)}"
+                )
+
+        def convert_fill_value(value, pa_type, dtype):
+            if value is None:
+                return value
+            if isinstance(value, (pa.Scalar, pa.Array, pa.ChunkedArray)):
+                return value
+            if is_array_like(value):
+                pa_box = pa.array
+            else:
+                pa_box = pa.scalar
+            try:
+                value = pa_box(value, type=pa_type, from_pandas=True)
+            except pa.ArrowTypeError as err:
+                msg = f"Invalid value '{str(value)}' for dtype {dtype}"
+                raise TypeError(msg) from err
+            return value
+
+        fill_value = convert_fill_value(value, self._data.type, self.dtype)
+
+        try:
+            if method is None:
+                return type(self)(pc.fill_null(self._data, fill_value=fill_value))
+            elif method == "pad":
+                return type(self)(pc.fill_null_forward(self._data))
+            elif method == "backfill":
+                return type(self)(pc.fill_null_backward(self._data))
+        except pa.ArrowNotImplementedError:
+            # ArrowNotImplementedError: Function 'coalesce' has no kernel
+            #   matching input types (duration[ns], duration[ns])
+            # TODO: remove try/except wrapper if/when pyarrow implements
+            #   a kernel for duration types.
+            pass
+
+        return super().fillna(value=value, method=method, limit=limit)
+
     def isin(self, values) -> npt.NDArray[np.bool_]:
         # short-circuit to return all False array.
         if not len(values):

pandas/tests/arrays/string_/test_string.py

@@ -408,14 +408,6 @@ def test_min_max_numpy(method, box, dtype, request):
 def test_fillna_args(dtype, request):
     # GH 37987
 
-    if dtype.storage == "pyarrow":
-        reason = (
-            "Regex pattern \"Cannot set non-string value '1' into "
-            "a StringArray.\" does not match 'Scalar must be NA or str'"
-        )
-        mark = pytest.mark.xfail(raises=AssertionError, reason=reason)
-        request.node.add_marker(mark)
-
     arr = pd.array(["a", pd.NA], dtype=dtype)
 
     res = arr.fillna(value="b")
@@ -426,8 +418,13 @@ def test_fillna_args(dtype, request):
     expected = pd.array(["a", "b"], dtype=dtype)
     tm.assert_extension_array_equal(res, expected)
 
-    msg = "Cannot set non-string value '1' into a StringArray."
-    with pytest.raises(ValueError, match=msg):
+    if dtype.storage == "pyarrow":
+        err = TypeError
+        msg = "Invalid value '1' for dtype string"
+    else:
+        err = ValueError
+        msg = "Cannot set non-string value '1' into a StringArray."
+    with pytest.raises(err, match=msg):
         arr.fillna(value=1)