BUG: DataFrame.min/max with axis=1 and uniform datetime64[ns, tz] types does not return NaNs

doc/source/whatsnew/v0.24.0.rst

@@ -1647,6 +1647,7 @@ Timezones
 - Bug in :meth:`DataFrame.any` returns wrong value when ``axis=1`` and the data is of datetimelike type (:issue:`23070`)
 - Bug in :meth:`DatetimeIndex.to_period` where a timezone aware index was converted to UTC first before creating :class:`PeriodIndex` (:issue:`22905`)
 - Bug in :meth:`DataFrame.tz_localize`, :meth:`DataFrame.tz_convert`, :meth:`Series.tz_localize`, and :meth:`Series.tz_convert` where ``copy=False`` would mutate the original argument inplace (:issue:`6326`)
+- Bug in :meth:`DataFrame.max` and :meth:`DataFrame.min` with ``axis=1`` where a :class:`Series` with ``NaN`` would be returned when all columns contained the same timezone (:issue:`10390`)
 
 Offsets
 ^^^^^^^

pandas/core/frame.py

@@ -7390,7 +7390,9 @@ def f(x):
             return op(x, axis=axis, skipna=skipna, **kwds)
 
         # exclude timedelta/datetime unless we are uniform types
-        if axis == 1 and self._is_mixed_type and self._is_datelike_mixed_type:
+        if (axis == 1 and self._is_datelike_mixed_type
+                and (self._is_mixed_type
+                     and not self._is_all_same_datetimetz_types)):
             numeric_only = True
 
         if numeric_only is None:

pandas/core/generic.py

@@ -5164,6 +5164,11 @@ def _is_datelike_mixed_type(self):
         f = lambda: self._data.is_datelike_mixed_type
         return self._protect_consolidate(f)
 
+    @property
+    def _is_all_same_datetimetz_types(self):
+        f = lambda: self._data.all_same_datetimetz_types
+        return self._protect_consolidate(f)
+
     def _check_inplace_setting(self, value):
         """ check whether we allow in-place setting with this type of value """
 

pandas/core/internals/managers.py

@@ -639,6 +639,16 @@ def is_view(self):
 
         return False
 
+    @property
+    def all_same_datetimetz_types(self):
+        """Whether all blocks are datetimetz and the same timezone"""
+        dtypes = set()
+        for block in self.blocks:
+            if not block.is_datetimetz or len(dtypes) > 1:
+                return False
+            dtypes.add(block.dtype)
+        return len(dtypes) == 1
+
     def get_bool_data(self, copy=False):
         """
         Parameters

pandas/tests/frame/test_timezones.py

@@ -196,3 +196,15 @@ def test_tz_localize_convert_copy_inplace_mutate(self, copy, method, tz):
                              index=date_range('20131027', periods=5,
                                               freq='1H', tz=tz))
         tm.assert_frame_equal(result, expected)
+
+    @pytest.mark.parametrize('op, expected_col', [
+        ['max', 'a'], ['min', 'b']
+    ])
+    def test_same_tz_min_max_axis_1(self, op, expected_col):
+        # GH 10390
+        df = DataFrame(date_range('2016-01-01 00:00:00', periods=3, tz='UTC'),
+                       columns=['a'])
+        df['b'] = df.a.subtract(pd.Timedelta(seconds=3600))
+        result = getattr(df, op)(axis=1)
+        expected = df[expected_col]
+        tm.assert_series_equal(result, expected)