BUG: Series/Index results in datetime/timedelta incorrectly if inputs are all nan/nat like

doc/source/whatsnew/v0.19.0.txt

@@ -484,8 +484,9 @@ Bug Fixes
 
 - Bug in ``Series.str.extractall()`` with ``str`` index raises ``ValueError``  (:issue:`13156`)
 - Bug in ``Series.str.extractall()`` with single group and quantifier  (:issue:`13382`)
-
 - Bug in ``DatetimeIndex`` and ``Period`` subtraction raises ``ValueError`` or ``AttributeError`` rather than ``TypeError`` (:issue:`13078`)
+- Bug in ``Index`` and ``Series`` created with ``NaN`` and ``NaT`` mixed data may not have ``datetime64`` dtype  (:issue:`13324`)
+- Bug in ``Index`` and ``Series`` may ignore ``np.datetime64('nat')`` and ``np.timdelta64('nat')`` to infer dtype (:issue:`13324`)
 - Bug in ``PeriodIndex`` and ``Period`` subtraction raises ``AttributeError`` (:issue:`13071`)
 - Bug in ``PeriodIndex`` construction returning a ``float64`` index in some circumstances (:issue:`13067`)
 - Bug in ``.resample(..)`` with a ``PeriodIndex`` not changing its ``freq`` appropriately when empty (:issue:`13067`)

pandas/indexes/base.py

@@ -242,8 +242,7 @@ def __new__(cls, data=None, dtype=None, copy=False, name=None,
                     # don't support boolean explicity ATM
                     pass
                 elif inferred != 'string':
-                    if (inferred.startswith('datetime') or
-                            tslib.is_timestamp_array(subarr)):
+                    if inferred.startswith('datetime'):
 
                         if (lib.is_datetime_with_singletz_array(subarr) or
                                 'tz' in kwargs):

pandas/src/inference.pyx

@@ -103,6 +103,7 @@ def infer_dtype(object _values):
         Py_ssize_t i, n
         object val
         ndarray values
+        bint seen_pdnat = False, seen_val = False
 
     if isinstance(_values, np.ndarray):
         values = _values
@@ -141,17 +142,34 @@ def infer_dtype(object _values):
     values = values.ravel()
 
     # try to use a valid value
-    for i in range(n):
-       val = util.get_value_1d(values, i)
-       if not is_null_datetimelike(val):
-           break
+    for i from 0 <= i < n:
+        val = util.get_value_1d(values, i)
 
-    if util.is_datetime64_object(val) or val is NaT:
+        # do not use is_nul_datetimelike to keep
+        # np.datetime64('nat') and np.timedelta64('nat')
+        if util._checknull(val):
+            pass
+        elif val is NaT:
+            seen_pdnat = True
+        else:
+            seen_val = True
+            break
+
+    # if all values are nan/NaT
+    if seen_val is False and seen_pdnat is True:
+        return 'datetime'
+        # float/object nan is handled in latter logic
+
+    if util.is_datetime64_object(val):
         if is_datetime64_array(values):
             return 'datetime64'
         elif is_timedelta_or_timedelta64_array(values):
             return 'timedelta'
 
+    elif is_timedelta(val):
+        if is_timedelta_or_timedelta64_array(values):
+            return 'timedelta'
+
     elif util.is_integer_object(val):
         # a timedelta will show true here as well
         if is_timedelta(val):
@@ -200,17 +218,15 @@ def infer_dtype(object _values):
         if is_bytes_array(values):
             return 'bytes'
 
-    elif is_timedelta(val):
-        if is_timedelta_or_timedelta64_array(values):
-            return 'timedelta'
-
     elif is_period(val):
         if is_period_array(values):
             return 'period'
 
     for i in range(n):
         val = util.get_value_1d(values, i)
-        if util.is_integer_object(val):
+        if (util.is_integer_object(val) and
+            not util.is_timedelta64_object(val) and
+            not util.is_datetime64_object(val)):
             return 'mixed-integer'
 
     return 'mixed'
@@ -237,20 +253,46 @@ def is_possible_datetimelike_array(object arr):
            return False
     return seen_datetime or seen_timedelta
 
+
 cdef inline bint is_null_datetimelike(v):
     # determine if we have a null for a timedelta/datetime (or integer versions)x
     if util._checknull(v):
         return True
+    elif v is NaT:
+        return True
     elif util.is_timedelta64_object(v):
         return v.view('int64') == iNaT
     elif util.is_datetime64_object(v):
         return v.view('int64') == iNaT
     elif util.is_integer_object(v):
         return v == iNaT
+    return False
+
+
+cdef inline bint is_null_datetime64(v):
+    # determine if we have a null for a datetime (or integer versions)x,
+    # excluding np.timedelta64('nat')
+    if util._checknull(v):
+        return True
+    elif v is NaT:
+        return True
+    elif util.is_datetime64_object(v):
+        return v.view('int64') == iNaT
+    return False
+
+
+cdef inline bint is_null_timedelta64(v):
+    # determine if we have a null for a timedelta (or integer versions)x,
+    # excluding np.datetime64('nat')
+    if util._checknull(v):
+        return True
     elif v is NaT:
         return True
+    elif util.is_timedelta64_object(v):
+        return v.view('int64') == iNaT
     return False
 
+
 cdef inline bint is_datetime(object o):
     return PyDateTime_Check(o)
 
@@ -420,7 +462,7 @@ def is_datetime_array(ndarray[object] values):
     # return False for all nulls
     for i in range(n):
         v = values[i]
-        if is_null_datetimelike(v):
+        if is_null_datetime64(v):
             # we are a regular null
             if util._checknull(v):
                null_count += 1
@@ -437,7 +479,7 @@ def is_datetime64_array(ndarray values):
     # return False for all nulls
     for i in range(n):
         v = values[i]
-        if is_null_datetimelike(v):
+        if is_null_datetime64(v):
             # we are a regular null
             if util._checknull(v):
                 null_count += 1
@@ -481,7 +523,7 @@ def is_timedelta_array(ndarray values):
         return False
     for i in range(n):
         v = values[i]
-        if is_null_datetimelike(v):
+        if is_null_timedelta64(v):
             # we are a regular null
             if util._checknull(v):
                 null_count += 1
@@ -496,7 +538,7 @@ def is_timedelta64_array(ndarray values):
         return False
     for i in range(n):
         v = values[i]
-        if is_null_datetimelike(v):
+        if is_null_timedelta64(v):
             # we are a regular null
             if util._checknull(v):
                 null_count += 1
@@ -512,7 +554,7 @@ def is_timedelta_or_timedelta64_array(ndarray values):
         return False
     for i in range(n):
         v = values[i]
-        if is_null_datetimelike(v):
+        if is_null_timedelta64(v):
             # we are a regular null
             if util._checknull(v):
                 null_count += 1

pandas/src/util.pxd

@@ -98,4 +98,4 @@ cdef inline bint _checknan(object val):
     return not cnp.PyArray_Check(val) and val != val
 
 cdef inline bint is_period_object(object val):
-    return getattr(val,'_typ','_typ') == 'period'
+    return getattr(val, '_typ', '_typ') == 'period'

pandas/tests/indexes/test_base.py

@@ -203,6 +203,49 @@ def __array__(self, dtype=None):
             result = pd.Index(ArrayLike(array))
             self.assert_index_equal(result, expected)
 
+    def test_index_ctor_infer_nan_nat(self):
+        # GH 13467
+        exp = pd.Float64Index([np.nan, np.nan])
+        self.assertEqual(exp.dtype, np.float64)
+        tm.assert_index_equal(Index([np.nan, np.nan]), exp)
+        tm.assert_index_equal(Index(np.array([np.nan, np.nan])), exp)
+
+        exp = pd.DatetimeIndex([pd.NaT, pd.NaT])
+        self.assertEqual(exp.dtype, 'datetime64[ns]')
+        tm.assert_index_equal(Index([pd.NaT, pd.NaT]), exp)
+        tm.assert_index_equal(Index(np.array([pd.NaT, pd.NaT])), exp)
+
+        exp = pd.DatetimeIndex([pd.NaT, pd.NaT])
+        self.assertEqual(exp.dtype, 'datetime64[ns]')
+
+        for data in [[pd.NaT, np.nan], [np.nan, pd.NaT],
+                     [np.nan, np.datetime64('nat')],
+                     [np.datetime64('nat'), np.nan]]:
+            tm.assert_index_equal(Index(data), exp)
+            tm.assert_index_equal(Index(np.array(data, dtype=object)), exp)
+
+        exp = pd.TimedeltaIndex([pd.NaT, pd.NaT])
+        self.assertEqual(exp.dtype, 'timedelta64[ns]')
+
+        for data in [[np.nan, np.timedelta64('nat')],
+                     [np.timedelta64('nat'), np.nan],
+                     [pd.NaT, np.timedelta64('nat')],
+                     [np.timedelta64('nat'), pd.NaT]]:
+
+            tm.assert_index_equal(Index(data), exp)
+            tm.assert_index_equal(Index(np.array(data, dtype=object)), exp)
+
+        # mixed np.datetime64/timedelta64 nat results in object
+        data = [np.datetime64('nat'), np.timedelta64('nat')]
+        exp = pd.Index(data, dtype=object)
+        tm.assert_index_equal(Index(data), exp)
+        tm.assert_index_equal(Index(np.array(data, dtype=object)), exp)
+
+        data = [np.timedelta64('nat'), np.datetime64('nat')]
+        exp = pd.Index(data, dtype=object)
+        tm.assert_index_equal(Index(data), exp)
+        tm.assert_index_equal(Index(np.array(data, dtype=object)), exp)
+
     def test_index_ctor_infer_periodindex(self):
         xp = period_range('2012-1-1', freq='M', periods=3)
         rs = Index(xp)

pandas/tests/series/test_constructors.py

@@ -252,6 +252,24 @@ def test_constructor_pass_none(self):
         expected = Series(index=Index([None]))
         assert_series_equal(s, expected)
 
+    def test_constructor_pass_nan_nat(self):
+        # GH 13467
+        exp = Series([np.nan, np.nan], dtype=np.float64)
+        self.assertEqual(exp.dtype, np.float64)
+        tm.assert_series_equal(Series([np.nan, np.nan]), exp)
+        tm.assert_series_equal(Series(np.array([np.nan, np.nan])), exp)
+
+        exp = Series([pd.NaT, pd.NaT])
+        self.assertEqual(exp.dtype, 'datetime64[ns]')
+        tm.assert_series_equal(Series([pd.NaT, pd.NaT]), exp)
+        tm.assert_series_equal(Series(np.array([pd.NaT, pd.NaT])), exp)
+
+        tm.assert_series_equal(Series([pd.NaT, np.nan]), exp)
+        tm.assert_series_equal(Series(np.array([pd.NaT, np.nan])), exp)
+
+        tm.assert_series_equal(Series([np.nan, pd.NaT]), exp)
+        tm.assert_series_equal(Series(np.array([np.nan, pd.NaT])), exp)
+
     def test_constructor_cast(self):
         self.assertRaises(ValueError, Series, ['a', 'b', 'c'], dtype=float)
 
@@ -688,8 +706,9 @@ def test_constructor_dtype_timedelta64(self):
         td = Series([np.timedelta64(300000000), pd.NaT])
         self.assertEqual(td.dtype, 'timedelta64[ns]')
 
+        # because iNaT is int, not coerced to timedelta
         td = Series([np.timedelta64(300000000), tslib.iNaT])
-        self.assertEqual(td.dtype, 'timedelta64[ns]')
+        self.assertEqual(td.dtype, 'object')
 
         td = Series([np.timedelta64(300000000), np.nan])
         self.assertEqual(td.dtype, 'timedelta64[ns]')