From dd2907a8a19d4e03bffdaa0007da2d98994788b7 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <61934744+phofl@users.noreply.github.com>
Date: Sun, 26 Nov 2023 19:03:16 +0100
Subject: [PATCH 1/2] BUG: mode not preserving object dtype for string option

---
 doc/source/whatsnew/v2.1.4.rst         |  2 +-
 pandas/core/series.py                  |  6 +++++-
 pandas/tests/series/test_reductions.py | 10 ++++++++++
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/doc/source/whatsnew/v2.1.4.rst b/doc/source/whatsnew/v2.1.4.rst
index 543a9864ced26..c16883380b882 100644
--- a/doc/source/whatsnew/v2.1.4.rst
+++ b/doc/source/whatsnew/v2.1.4.rst
@@ -25,7 +25,7 @@ Bug fixes
 - Bug in :meth:`Index.__getitem__` returning wrong result for Arrow dtypes and negative stepsize (:issue:`55832`)
 - Fixed bug in :meth:`DataFrame.__setitem__` casting :class:`Index` with object-dtype to PyArrow backed strings when ``infer_string`` option is set (:issue:`55638`)
 - Fixed bug in :meth:`Index.insert` casting object-dtype to PyArrow backed strings when ``infer_string`` option is set (:issue:`55638`)
--
+- Fixed bug in :meth:`Series.mode` not keeping object dtype when ``infer_string`` is set (:issue:`56183`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_214.other:
diff --git a/pandas/core/series.py b/pandas/core/series.py
index a9679f22f9933..2eb491b937871 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -2287,7 +2287,11 @@ def mode(self, dropna: bool = True) -> Series:
 
         # Ensure index is type stable (should always use int index)
         return self._constructor(
-            res_values, index=range(len(res_values)), name=self.name, copy=False
+            res_values,
+            index=range(len(res_values)),
+            name=self.name,
+            copy=False,
+            dtype=self.dtype,
         ).__finalize__(self, method="mode")
 
     def unique(self) -> ArrayLike:  # pylint: disable=useless-parent-delegation
diff --git a/pandas/tests/series/test_reductions.py b/pandas/tests/series/test_reductions.py
index 4bbbcf3bf54c2..76353ab25fca6 100644
--- a/pandas/tests/series/test_reductions.py
+++ b/pandas/tests/series/test_reductions.py
@@ -51,6 +51,16 @@ def test_mode_nullable_dtype(any_numeric_ea_dtype):
     tm.assert_series_equal(result, expected)
 
 
+def test_mode_infer_string():
+    # GH#56183
+    pytest.importorskip("pyarrow")
+    ser = Series(["a", "b"], dtype=object)
+    with pd.option_context("future.infer_string", True):
+        result = ser.mode()
+    expected = Series(["a", "b"], dtype=object)
+    tm.assert_series_equal(result, expected)
+
+
 def test_reductions_td64_with_nat():
     # GH#8617
     ser = Series([0, pd.NaT], dtype="m8[ns]")

From ff719b884438ee1740a41e7f5230d7c6fdbf6ad2 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <61934744+phofl@users.noreply.github.com>
Date: Sun, 26 Nov 2023 19:05:41 +0100
Subject: [PATCH 2/2] Adjust tests in root directory for new string option

---
 pandas/tests/test_algos.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/pandas/tests/test_algos.py b/pandas/tests/test_algos.py
index a6e63dfd5f409..f4445073ad3a1 100644
--- a/pandas/tests/test_algos.py
+++ b/pandas/tests/test_algos.py
@@ -1675,7 +1675,7 @@ class TestHashTable:
     def test_hashtable_unique(self, htable, tm_dtype, writable):
         # output of maker has guaranteed unique elements
         maker = getattr(tm, "make" + tm_dtype + "Index")
-        s = Series(maker(1000))
+        s = Series(maker(1000), dtype=None if tm_dtype != "String" else object)
         if htable == ht.Float64HashTable:
             # add NaN for float column
             s.loc[500] = np.nan
@@ -1715,7 +1715,7 @@ def test_hashtable_unique(self, htable, tm_dtype, writable):
     def test_hashtable_factorize(self, htable, tm_dtype, writable):
         # output of maker has guaranteed unique elements
         maker = getattr(tm, "make" + tm_dtype + "Index")
-        s = Series(maker(1000))
+        s = Series(maker(1000), dtype=None if tm_dtype != "String" else object)
         if htable == ht.Float64HashTable:
             # add NaN for float column
             s.loc[500] = np.nan
@@ -1948,7 +1948,7 @@ def test_timedelta_mode(self):
         tm.assert_series_equal(ser.mode(), exp)
 
     def test_mixed_dtype(self):
-        exp = Series(["foo"])
+        exp = Series(["foo"], dtype=object)
         ser = Series([1, "foo", "foo"])
         tm.assert_numpy_array_equal(algos.mode(ser.values), exp.values)
         tm.assert_series_equal(ser.mode(), exp)