BUG: DatetimeIndex with freq raises ValueError when passed value is too short

Author: sinhrks

doc/source/release.rst

@@ -499,6 +499,7 @@ Bug Fixes
 - Bug in ``MultiIndex.get_level_values`` doesn't preserve ``DatetimeIndex`` and ``PeriodIndex`` attributes (:issue:`7092`)
 - Bug in ``Groupby`` doesn't preserve ``tz`` (:issue:`3950`)
 - Bug in ``PeriodIndex`` partial string slicing (:issue:`6716`)
+- Bug in ``DatetimeIndex`` specifying ``freq`` raises ``ValueError`` when passed value is too short
 
 pandas 0.13.1
 -------------

pandas/tseries/index.py

@@ -299,8 +299,10 @@ def __new__(cls, data=None,
             if freq is not None and not freq_infer:
                 inferred = subarr.inferred_freq
                 if inferred != freq.freqstr:
-                    raise ValueError('Dates do not conform to passed '
-                                     'frequency')
+                    on_freq = cls._generate(subarr[0], None, len(subarr), None, freq, tz=tz)
+                    if not np.array_equal(subarr.asi8, on_freq.asi8):
+                        raise ValueError('Inferred frequency {0} from passed dates does not'
+                                         'conform to passed frequency {1}'.format(inferred, freq.freqstr))
 
         if freq_infer:
             inferred = subarr.inferred_freq

pandas/tseries/tests/test_period.py

@@ -2314,6 +2314,11 @@ def test_factorize(self):
         self.assert_numpy_array_equal(arr, exp_arr)
         self.assert_(idx.equals(exp_idx))
 
+    def test_recreate_from_data(self):
+        for o in ['M', 'Q', 'A', 'D', 'B', 'T', 'S', 'L', 'U', 'N', 'H']:
+            org = PeriodIndex(start='2001/04/01', freq=o, periods=1)
+            idx = PeriodIndex(org.values, freq=o)
+            self.assert_(idx.equals(org))
 
 def _permute(obj):
     return obj.take(np.random.permutation(len(obj)))

pandas/tseries/tests/test_timeseries.py

@@ -285,6 +285,28 @@ def test_indexing(self):
         # this is a single date, so will raise
         self.assertRaises(KeyError, df.__getitem__, df.index[2],)
 
+    def test_recreate_from_data(self):
+        if _np_version_under1p7:
+            freqs = ['M', 'Q', 'A', 'D', 'B', 'T', 'S', 'L', 'U', 'H']
+        else:
+            freqs = ['M', 'Q', 'A', 'D', 'B', 'T', 'S', 'L', 'U', 'H', 'N', 'C']
+
+        for f in freqs:
+            org = DatetimeIndex(start='2001/02/01 09:00', freq=f, periods=1)
+            idx = DatetimeIndex(org, freq=f)
+            self.assert_(idx.equals(org))
+
+        # unbale to create tz-aware 'A' and 'C' freq
+        if _np_version_under1p7:
+            freqs = ['M', 'Q', 'D', 'B', 'T', 'S', 'L', 'U', 'H']
+        else:
+            freqs = ['M', 'Q', 'D', 'B', 'T', 'S', 'L', 'U', 'H', 'N']
+
+        for f in freqs:
+            org = DatetimeIndex(start='2001/02/01 09:00', freq=f, tz='US/Pacific', periods=1)
+            idx = DatetimeIndex(org, freq=f, tz='US/Pacific')
+            self.assert_(idx.equals(org))
+
 
 def assert_range_equal(left, right):
     assert(left.equals(right))