Series.describe returns first and last for tz-aware datetimes

GH issue 21328

Author: louispotok

pandas/core/generic.py

@@ -20,7 +20,7 @@
     is_bool_dtype,
     is_categorical_dtype,
     is_numeric_dtype,
-    is_datetime64_dtype,
+    is_datetime64_any_dtype,
     is_timedelta64_dtype,
     is_datetime64tz_dtype,
     is_list_like,
@@ -8530,12 +8530,13 @@ def describe_categorical_1d(data):
             if result[1] > 0:
                 top, freq = objcounts.index[0], objcounts.iloc[0]
 
-                if is_datetime64_dtype(data):
+                if is_datetime64_any_dtype(data):
+                    tz = data.dt.tz
                     asint = data.dropna().values.view('i8')
                     names += ['top', 'freq', 'first', 'last']
-                    result += [tslib.Timestamp(top), freq,
-                               tslib.Timestamp(asint.min()),
-                               tslib.Timestamp(asint.max())]
+                    result += [tslib.Timestamp(top, tz=tz), freq,
+                               tslib.Timestamp(asint.min(), tz=tz),
+                               tslib.Timestamp(asint.max(), tz=tz)]
                 else:
                     names += ['top', 'freq']
                     result += [top, freq]

pandas/tests/series/test_analytics.py

@@ -336,6 +336,31 @@ def test_describe(self):
                           index=['count', 'unique', 'top', 'freq'])
         tm.assert_series_equal(result, expected)
 
+        start = Timestamp(2018, 1, 1)
+        end = Timestamp(2018, 1, 5)
+        s = Series(date_range(start, end), name="tz-naive")
+        result = s.describe()
+        expected = Series(
+            [5, 5, start, 1, start, end],
+            name="tz-naive",
+            index=['count', 'unique', 'top', 'freq', 'first', 'last']
+        )
+        tm.assert_series_equal(result, expected)
+
+        start = Timestamp(2018, 1, 1)
+        end = Timestamp(2018, 1, 5)
+        tz = "US/Eastern"
+        s = Series(date_range(start, end, tz=tz), name="tz-aware")
+        result = s.describe()
+        expected = Series(
+            [5, 5, start.tz_localize(tz), 1, start.tz_localize(tz),
+             end.tz_localize(tz)
+             ],
+            name="tz-aware",
+            index=['count', 'unique', 'top', 'freq', 'first', 'last']
+        )
+        tm.assert_series_equal(result, expected)
+
     def test_argsort(self):
         self._check_accum_op('argsort', check_dtype=False)
         argsorted = self.ts.argsort()