[ENH] nargsort handles EA with its _values_for_argsort

doc/source/whatsnew/v0.25.0.rst

@@ -133,6 +133,7 @@ Other Enhancements
 - :meth:`DataFrame.describe` now formats integer percentiles without decimal point (:issue:`26660`)
 - Added support for reading SPSS .sav files using :func:`read_spss` (:issue:`26537`)
 - Added new option ``plotting.backend`` to be able to select a plotting backend different than the existing ``matplotlib`` one. Use ``pandas.set_option('plotting.backend', '<backend-module>')`` where ``<backend-module`` is a library implementing the pandas plotting API (:issue:`14130`)
+- :meth:`nargsort` handles ``ExtensionArray`` without calling ``np.asanyarray`` (:issue:`25439`)
 
 .. _whatsnew_0250.api_breaking:
 

pandas/core/sorting.py

@@ -1,6 +1,4 @@
 """ miscellaneous sorting / groupby utilities """
-import warnings
-
 import numpy as np
 
 from pandas._libs import algos, hashtable, lib
@@ -9,7 +7,8 @@
 from pandas.core.dtypes.cast import infer_dtype_from_array
 from pandas.core.dtypes.common import (
     ensure_int64, ensure_platform_int, is_categorical_dtype,
-    is_extension_array_dtype, is_list_like)
+    is_extension_array_dtype, is_list_like, is_sparse)
+from pandas.core.dtypes.generic import ABCIndexClass
 from pandas.core.dtypes.missing import isna
 
 import pandas.core.algorithms as algorithms
@@ -239,12 +238,12 @@ def nargsort(items, kind='quicksort', ascending=True, na_position='last'):
     GH #6399, #5231
     """
 
+    mask = isna(items)
     # specially handle Categorical
     if is_categorical_dtype(items):
         if na_position not in {'first', 'last'}:
             raise ValueError('invalid na_position: {!r}'.format(na_position))
 
-        mask = isna(items)
         cnt_null = mask.sum()
         sorted_idx = items.argsort(ascending=ascending, kind=kind)
         if ascending and na_position == 'last':
@@ -255,15 +254,19 @@ def nargsort(items, kind='quicksort', ascending=True, na_position='last'):
             sorted_idx = np.roll(sorted_idx, cnt_null)
         return sorted_idx
 
-    with warnings.catch_warnings():
-        # https://github.com/pandas-dev/pandas/issues/25439
-        # can be removed once ExtensionArrays are properly handled by nargsort
-        warnings.filterwarnings(
-            "ignore", category=FutureWarning,
-            message="Converting timezone-aware DatetimeArray to")
+    if (not isinstance(items, ABCIndexClass)
+            and is_extension_array_dtype(items)):
+
+        if is_sparse(items):
+            # The conversion to np.ndarray is due to the fact that
+            # SparseArray.isna() is also a SparseArray
+            mask = np.array(isna(items))
+
+        items = items._values_for_argsort()
+    else:
         items = np.asanyarray(items)
+
     idx = np.arange(len(items))
-    mask = isna(items)
     non_nans = items[~mask]
     non_nan_idx = idx[~mask]
     nan_idx = np.nonzero(mask)[0]

pandas/tests/extension/base/methods.py

@@ -2,6 +2,7 @@
 import pytest
 
 import pandas as pd
+from pandas.core.sorting import nargsort
 import pandas.util.testing as tm
 
 from .base import BaseExtensionTests
@@ -44,6 +45,15 @@ def test_argsort_missing(self, data_missing_for_sorting):
         expected = pd.Series(np.array([1, -1, 0], dtype=np.int64))
         self.assert_series_equal(result, expected)
 
+    @pytest.mark.parametrize('na_position, expected', [
+        ('last', np.array([2, 0, 1])),
+        ('first', np.array([1, 2, 0]))
+    ])
+    def test_nargsort(self, data_missing_for_sorting, na_position, expected):
+        # GH 25439
+        result = nargsort(data_missing_for_sorting, na_position=na_position)
+        tm.assert_numpy_array_equal(result, expected, check_dtype=False)
+
     @pytest.mark.parametrize('ascending', [True, False])
     def test_sort_values(self, data_for_sorting, ascending):
         ser = pd.Series(data_for_sorting)

pandas/tests/test_sorting.py

@@ -6,8 +6,7 @@
 from numpy import nan
 import pytest
 
-from pandas import (
-    DataFrame, MultiIndex, Series, array, concat, merge, to_datetime)
+from pandas import DataFrame, MultiIndex, Series, array, concat, merge
 from pandas.core import common as com
 from pandas.core.sorting import (
     decons_group_index, get_group_index, is_int64_overflow_possible,
@@ -181,13 +180,6 @@ def test_nargsort(self):
         exp = list(range(5)) + list(range(105, 110)) + list(range(104, 4, -1))
         tm.assert_numpy_array_equal(result, np.array(exp), check_dtype=False)
 
-    def test_nargsort_datetimearray_warning(self):
-        # https://github.com/pandas-dev/pandas/issues/25439
-        # can be removed once the FutureWarning for np.array(DTA) is removed
-        data = to_datetime([0, 2, 0, 1]).tz_localize('Europe/Brussels')
-        with tm.assert_produces_warning(None):
-            nargsort(data)
-
 
 class TestMerge: