BUG: Bug in conversion of a string types to a DatetimeIndex with a specifed frequency (GH6273)

doc/source/release.rst

@@ -75,6 +75,7 @@ Bug Fixes
 - Inconsistent tz parsing Timestamp/to_datetime for current year (:issue:`5958`)
 - Indexing bugs with reordered indexes (:issue:`6252`, :issue:`6254`)
 - Bug in ``.xs`` with a Series multiindex (:issue:`6258`, :issue:`5684`)
+- Bug in conversion of a string types to a DatetimeIndex with a specified frequency (:issue:`6273`, :issue:`6274`)
 
 pandas 0.13.1
 -------------

pandas/tests/test_index.py

@@ -146,6 +146,31 @@ def test_constructor_corner(self):
         # corner case
         self.assertRaises(TypeError, Index, 0)
 
+    def test_constructor_from_series(self):
+
+        expected = DatetimeIndex([Timestamp('20110101'),Timestamp('20120101'),Timestamp('20130101')])
+        s = Series([Timestamp('20110101'),Timestamp('20120101'),Timestamp('20130101')])
+        result = Index(s)
+        self.assertTrue(result.equals(expected))
+        result = DatetimeIndex(s)
+        self.assertTrue(result.equals(expected))
+
+        # GH 6273
+        # create from a series, passing a freq
+        s = Series(pd.to_datetime(['1-1-1990', '2-1-1990', '3-1-1990', '4-1-1990', '5-1-1990']))
+        result = DatetimeIndex(s, freq='MS')
+        expected = DatetimeIndex(['1-1-1990', '2-1-1990', '3-1-1990', '4-1-1990', '5-1-1990'],freq='MS')
+        self.assertTrue(result.equals(expected))
+
+        df = pd.DataFrame(np.random.rand(5,3))
+        df['date'] = ['1-1-1990', '2-1-1990', '3-1-1990', '4-1-1990', '5-1-1990']
+        result = DatetimeIndex(df['date'], freq='MS')
+
+        # GH 6274
+        # infer freq of same
+        result = pd.infer_freq(df['date'])
+        self.assertEqual(result,'MS')
+
     def test_index_ctor_infer_periodindex(self):
         from pandas import period_range, PeriodIndex
         xp = period_range('2012-1-1', freq='M', periods=3)

pandas/tseries/index.py

@@ -254,6 +254,11 @@ def __new__(cls, data=None,
         else:
             try:
                 subarr = tools.to_datetime(data, box=False)
+
+                # make sure that we have a index/ndarray like (and not a Series)
+                if isinstance(subarr, ABCSeries):
+                    subarr = subarr.values
+
             except ValueError:
                 # tz aware
                 subarr = tools.to_datetime(data, box=False, utc=True)