ENH: Arrow backed string array - implement factorize() method without casting to objects

asv_bench/benchmarks/algorithms.py

@@ -5,6 +5,7 @@
 from pandas._libs import lib
 
 import pandas as pd
+from pandas.core.arrays.string_arrow import ArrowStringDtype
 
 from .pandas_vb_common import tm
 
@@ -43,23 +44,34 @@ class Factorize:
  "datetime64[ns, tz]",
  "Int64",
  "boolean",
+ "string_arrow",
  ],
  ]
  param_names = ["unique", "sort", "dtype"]
 
  def setup(self, unique, sort, dtype):
  N = 10 ** 5
+ string_index = tm.makeStringIndex(N)
+ try:
+ string_arrow = pd.array(string_index, dtype=ArrowStringDtype())
+ except ImportError:
+ string_arrow = None
+
+ if dtype == "string_arrow" and not string_arrow:
+ raise NotImplementedError
+
  data = {
  "int": pd.Int64Index(np.arange(N)),
  "uint": pd.UInt64Index(np.arange(N)),
  "float": pd.Float64Index(np.random.randn(N)),
- "string": tm.makeStringIndex(N),
+ "string": string_index,
  "datetime64[ns]": pd.date_range("2011-01-01", freq="H", periods=N),
  "datetime64[ns, tz]": pd.date_range(
  "2011-01-01", freq="H", periods=N, tz="Asia/Tokyo"
  ),
  "Int64": pd.array(np.arange(N), dtype="Int64"),
  "boolean": pd.array(np.random.randint(0, 2, N), dtype="boolean"),
+ "string_arrow": string_arrow,
  }[dtype]
  if not unique:
  data = data.repeat(5)

pandas/core/arrays/string_arrow.py

@@ -6,6 +6,7 @@
  Any,
  Optional,
  Sequence,
+ Tuple,
  Type,
  Union,
 )
@@ -20,6 +21,7 @@
  Dtype,
  NpDtype,
 )
+from pandas.util._decorators import doc
 from pandas.util._validators import validate_fillna_kwargs
 
 from pandas.core.dtypes.base import ExtensionDtype
@@ -273,9 +275,22 @@ def __len__(self) -> int:
  """
  return len(self._data)
 
- @classmethod
- def _from_factorized(cls, values, original):
- return cls._from_sequence(values)
+ @doc(ExtensionArray.factorize)
+ def factorize(self, na_sentinel: int = -1) -> Tuple[np.ndarray, ExtensionArray]:
+ encoded = self._data.dictionary_encode()
+ indices = pa.chunked_array(
+ [c.indices for c in encoded.chunks], type=encoded.type.index_type
+ ).to_pandas()
+ if indices.dtype.kind == "f":
+ indices[np.isnan(indices)] = na_sentinel
+ indices = indices.astype(np.int64, copy=False)
+
+ if encoded.num_chunks:
+ uniques = type(self)(encoded.chunk(0).dictionary)
+ else:
+ uniques = type(self)(pa.array([], type=encoded.type.value_type))
+
+ return indices.values, uniques
 
  @classmethod
  def _concat_same_type(cls, to_concat) -> ArrowStringArray:

pandas/tests/extension/test_string.py

@@ -26,6 +26,29 @@
 from pandas.tests.extension import base
 
 
+def split_array(arr):
+ if not isinstance(arr.dtype, ArrowStringDtype):
+ pytest.skip("chunked array n/a")
+
+ def _split_array(arr):
+ import pyarrow as pa
+
+ arrow_array = arr._data
+ split = len(arrow_array) // 2
+ arrow_array = pa.chunked_array(
+ [*arrow_array[:split].chunks, *arrow_array[split:].chunks]
+ )
+ assert arrow_array.num_chunks == 2
+ return type(arr)(arrow_array)
+
+ return _split_array(arr)
+
+
+@pytest.fixture(params=[True, False])
+def chunked(request):
+ return request.param
+
+
 @pytest.fixture(
  params=[
  StringDtype,
@@ -39,28 +62,32 @@ def dtype(request):
 
 
 @pytest.fixture
-def data(dtype):
+def data(dtype, chunked):
  strings = np.random.choice(list(string.ascii_letters), size=100)
  while strings[0] == strings[1]:
  strings = np.random.choice(list(string.ascii_letters), size=100)
 
- return dtype.construct_array_type()._from_sequence(strings)
+ arr = dtype.construct_array_type()._from_sequence(strings)
+ return split_array(arr) if chunked else arr
 
 
 @pytest.fixture
-def data_missing(dtype):
+def data_missing(dtype, chunked):
  """Length 2 array with [NA, Valid]"""
- return dtype.construct_array_type()._from_sequence([pd.NA, "A"])
+ arr = dtype.construct_array_type()._from_sequence([pd.NA, "A"])
+ return split_array(arr) if chunked else arr
 
 
 @pytest.fixture
-def data_for_sorting(dtype):
- return dtype.construct_array_type()._from_sequence(["B", "C", "A"])
+def data_for_sorting(dtype, chunked):
+ arr = dtype.construct_array_type()._from_sequence(["B", "C", "A"])
+ return split_array(arr) if chunked else arr
 
 
 @pytest.fixture
-def data_missing_for_sorting(dtype):
- return dtype.construct_array_type()._from_sequence(["B", pd.NA, "A"])
+def data_missing_for_sorting(dtype, chunked):
+ arr = dtype.construct_array_type()._from_sequence(["B", pd.NA, "A"])
+ return split_array(arr) if chunked else arr
 
 
 @pytest.fixture
@@ -69,10 +96,11 @@ def na_value():
 
 
 @pytest.fixture
-def data_for_grouping(dtype):
- return dtype.construct_array_type()._from_sequence(
+def data_for_grouping(dtype, chunked):
+ arr = dtype.construct_array_type()._from_sequence(
  ["B", "B", pd.NA, pd.NA, "A", "A", "B", "C"]
  )
+ return split_array(arr) if chunked else arr
 
 
 class TestDtype(base.BaseDtypeTests):