BUG: DataFrame.rank does not return EA types when original type was an EADtype

doc/source/whatsnew/v3.0.0.rst

@@ -204,6 +204,7 @@ Other enhancements
 - :meth:`.DataFrameGroupBy.transform`, :meth:`.SeriesGroupBy.transform`, :meth:`.DataFrameGroupBy.agg`, :meth:`.SeriesGroupBy.agg`, :meth:`.SeriesGroupBy.apply`, :meth:`.DataFrameGroupBy.apply` now support ``kurt`` (:issue:`40139`)
 - :meth:`DataFrame.apply` supports using third-party execution engines like the Bodo.ai JIT compiler (:issue:`60668`)
 - :meth:`DataFrame.iloc` and :meth:`Series.iloc` now support boolean masks in ``__getitem__`` for more consistent indexing behavior (:issue:`60994`)
+- :meth:`DataFrame.rank` now preserves the dtype for extension arrays (:issue:`52829`)
 - :meth:`DataFrame.to_csv` and :meth:`Series.to_csv` now support Python's new-style format strings (e.g., ``"{:.6f}"``) for the ``float_format`` parameter, in addition to old-style ``%`` format strings and callables. This allows for more flexible and modern formatting of floating point numbers when exporting to CSV. (:issue:`49580`)
 - :meth:`DataFrameGroupBy.transform`, :meth:`SeriesGroupBy.transform`, :meth:`DataFrameGroupBy.agg`, :meth:`SeriesGroupBy.agg`, :meth:`RollingGroupby.apply`, :meth:`ExpandingGroupby.apply`, :meth:`Rolling.apply`, :meth:`Expanding.apply`, :meth:`DataFrame.apply` with ``engine="numba"`` now supports positional arguments passed as kwargs (:issue:`58995`)
 - :meth:`Rolling.agg`, :meth:`Expanding.agg` and :meth:`ExponentialMovingWindow.agg` now accept :class:`NamedAgg` aggregations through ``**kwargs`` (:issue:`28333`)

pandas/core/algorithms.py

@@ -1088,7 +1088,6 @@ def rank(
         )
     else:
         raise TypeError("Array with ndim > 2 are not supported.")
-
     return ranks
 
 

pandas/core/arrays/base.py

@@ -2408,6 +2408,7 @@ def _rank(
         """
         See Series.rank.__doc__.
         """
+
         if axis != 0:
             raise NotImplementedError
 

pandas/core/generic.py

@@ -9276,34 +9276,35 @@ def rank(
             msg = "na_option must be one of 'keep', 'top', or 'bottom'"
             raise ValueError(msg)
 
-        def ranker(data):
-            if data.ndim == 2:
-                # i.e. DataFrame, we cast to ndarray
-                values = data.values
-            else:
-                # i.e. Series, can dispatch to EA
-                values = data._values
-
-            if isinstance(values, ExtensionArray):
-                ranks = values._rank(
-                    axis=axis_int,
+        def ranker(blk_values):
+            if isinstance(blk_values, ExtensionArray) and blk_values.ndim == 1:
+                ranks = blk_values._rank(
+                    axis=0,
                     method=method,
                     ascending=ascending,
                     na_option=na_option,
                     pct=pct,
                 )
             else:
-                ranks = algos.rank(
-                    values,
-                    axis=axis_int,
-                    method=method,
-                    ascending=ascending,
-                    na_option=na_option,
-                    pct=pct,
-                )
-
-            ranks_obj = self._constructor(ranks, **data._construct_axes_dict())
-            return ranks_obj.__finalize__(self, method="rank")
+                if axis_int == 0:
+                    ranks = algos.rank(
+                        blk_values.T,
+                        axis=axis_int,
+                        method=method,
+                        ascending=ascending,
+                        na_option=na_option,
+                        pct=pct,
+                    ).T
+                else:
+                    ranks = algos.rank(
+                        blk_values,
+                        axis=axis_int,
+                        method=method,
+                        ascending=ascending,
+                        na_option=na_option,
+                        pct=pct,
+                    )
+            return ranks
 
         if numeric_only:
             if self.ndim == 1 and not is_numeric_dtype(self.dtype):
@@ -9316,7 +9317,16 @@ def ranker(data):
         else:
             data = self
 
-        return ranker(data)
+        should_transpose = axis_int == 1
+
+        if should_transpose:
+            data = data.T
+        applied = data._mgr.apply(ranker)
+        result = self._constructor_from_mgr(applied, axes=applied.axes)
+        if should_transpose:
+            result = result.T
+
+        return result.__finalize__(self, method="rank")
 
     @doc(_shared_docs["compare"], klass=_shared_doc_kwargs["klass"])
     def compare(

pandas/tests/frame/methods/test_rank.py

@@ -10,6 +10,7 @@
     Infinity,
     NegInfinity,
 )
+import pandas.util._test_decorators as td
 
 from pandas import (
     DataFrame,
@@ -498,3 +499,49 @@ def test_rank_string_dtype(self, string_dtype_no_object):
             exp_dtype = "float64"
         expected = Series([1, 2, None, 3], dtype=exp_dtype)
         tm.assert_series_equal(result, expected)
+
+    @pytest.mark.parametrize(
+        "method,og_dtype,expected_dtype",
+        [
+            ("average", "UInt32", "Float64"),
+            ("average", "Float32", "Float64"),
+            pytest.param(
+                "average",
+                "int32[pyarrow]",
+                "double[pyarrow]",
+                marks=td.skip_if_no("pyarrow"),
+            ),
+            ("min", "Int32", "Float64"),
+            ("min", "Float32", "Float64"),
+            pytest.param(
+                "min",
+                "int32[pyarrow]",
+                "double[pyarrow]",
+                marks=td.skip_if_no("pyarrow"),
+            ),
+        ],
+    )
+    def test_rank_extension_array_dtype(self, method, og_dtype, expected_dtype):
+        # GH#52829
+        result = DataFrame([4, 89, 33], dtype=og_dtype).rank()
+        if method == "average":
+            expected = DataFrame([1.0, 3.0, 2.0], dtype=expected_dtype)
+        else:
+            expected = DataFrame([1, 3, 2], dtype=expected_dtype)
+        tm.assert_frame_equal(result, expected)
+
+    def test_rank_mixed_extension_array_dtype(self):
+        pytest.importorskip("pyarrow")
+        result = DataFrame(
+            {
+                "base": Series([4, 5, 6]),
+                "extension": Series([7, 8, 9], dtype="int32[pyarrow]"),
+            }
+        ).rank(method="min")
+        expected = DataFrame(
+            {
+                "base": Series([1.0, 2.0, 3.0], dtype="float64"),
+                "extension": Series([1, 2, 3], dtype="uint64[pyarrow]"),
+            }
+        )
+        tm.assert_frame_equal(result, expected)