BUG: fixup GH #2751; make sure that we cast to platform numeric

     when a list is specified; use the Series codepath
     for initial list conversion (change from using DataFrame)
TST: added test for overflow in df creation

Author: jreback

pandas/core/common.py

@@ -805,10 +805,11 @@ def _consensus_name_attr(objs):
 # Lots of little utilities
 
 
-def _possibly_convert_objects(values, convert_dates=True, convert_numeric=True):
+def _possibly_convert_objects(values, convert_dates=True, convert_numeric=True, convert_platform=False):
     """ if we have an object dtype, try to coerce dates and/or numers """
 
-    if values.dtype == np.object_ and convert_dates:
+    # convert dates
+    if convert_dates and getattr(values,'dtype',None) == np.object_:
 
         # we take an aggressive stance and convert to datetime64[ns]
         if convert_dates == 'coerce':
@@ -821,7 +822,8 @@ def _possibly_convert_objects(values, convert_dates=True, convert_numeric=True):
         else:
             values = lib.maybe_convert_objects(values, convert_datetime=convert_dates)
 
-    if values.dtype == np.object_ and convert_numeric:
+    # convert to numeric
+    if convert_numeric and getattr(values,'dtype',None) == np.object_:
         try:
             new_values = lib.maybe_convert_numeric(values,set(),coerce_numeric=True)
 
@@ -832,6 +834,14 @@ def _possibly_convert_objects(values, convert_dates=True, convert_numeric=True):
         except:
             pass
 
+    # platform conversion
+    #   allow ndarray or list here
+    if convert_platform:
+        if isinstance(values, (list,tuple)):
+            values = lib.list_to_object_array(values)
+        if values.dtype == np.object_:
+            values = lib.maybe_convert_objects(values)
+
     return values
 
 

pandas/core/frame.py

@@ -5460,11 +5460,21 @@ def _prep_ndarray(values, copy=True):
         if len(values) == 0:
             return np.empty((0, 0), dtype=object)
 
-        arr = np.asarray(values)
-        # NumPy strings are a pain, convert to object
-        if issubclass(arr.dtype.type, basestring):
-            arr = np.array(values, dtype=object, copy=True)
-        values = arr
+        def convert(v):
+            return com._possibly_convert_objects(v,
+                                                 convert_dates=False,
+                                                 convert_numeric=False,
+                                                 convert_platform=True)
+
+
+        # we could have a 1-dim or 2-dim list here
+        # this is equiv of np.asarray, but does object conversion
+        # and platform dtype preservation
+        if com.is_list_like(values[0]) or hasattr(values[0],'len'):
+            values = np.array([ convert(v) for v in values])
+        else:
+            values = convert(values)
+
     else:
         # drop subclass info, do not copy data
         values = np.asarray(values)

pandas/core/series.py

@@ -3111,11 +3111,15 @@ def _try_cast(arr):
                     raise
                 subarr = pa.array(data, dtype=object, copy=copy)
                 subarr = lib.maybe_convert_objects(subarr)
-                subarr = com._possibly_cast_to_datetime(subarr, dtype)
+            
         else:
-            subarr = lib.list_to_object_array(data)
-            subarr = lib.maybe_convert_objects(subarr)
-            subarr = com._possibly_cast_to_datetime(subarr, dtype)
+            subarr = com._possibly_convert_objects(data,
+                                                   convert_dates=False,
+                                                   convert_numeric=False,
+                                                   convert_platform=True)
+
+        subarr = com._possibly_cast_to_datetime(subarr, dtype)
+
     else:
         subarr = _try_cast(data)
 

pandas/tests/test_frame.py

@@ -8133,12 +8133,43 @@ def test_constructor_with_datetimes(self):
         expected.sort()
         assert_series_equal(result, expected)
 
-        # GH #2751 (construction with no index specified)
-        df = DataFrame({'a':[1,2,4,7], 'b':[1.2, 2.3, 5.1, 6.3], 'c':list('abcd'), 'd':[datetime(2000,1,1) for i in range(4)] })
+    def test_constructor_for_list_with_dtypes(self):
+        intname = np.dtype(np.int_).name
+        floatname = np.dtype(np.float_).name
+        datetime64name = np.dtype('M8[ns]').name
+        objectname = np.dtype(np.object_).name
+
+        # test list of lists/ndarrays
+        df = DataFrame([np.arange(5) for x in range(5)])
+        result = df.get_dtype_counts()
+        expected = Series({'int64' : 5})
+
+        df = DataFrame([np.array(np.arange(5),dtype='int32') for x in range(5)])
+        result = df.get_dtype_counts()
+        expected = Series({'int32' : 5})
+
+        # overflow issue? (we always expecte int64 upcasting here)
+        df = DataFrame({'a' : [2**31,2**31+1]})
+        result = df.get_dtype_counts()
+        expected = Series({'int64' : 1 })
+        assert_series_equal(result, expected)
+
+        # GH #2751 (construction with no index specified), make sure we cast to platform values
+        df = DataFrame([1, 2])
+        result = df.get_dtype_counts()
+        expected = Series({'int64': 1 })
+        assert_series_equal(result, expected)
+
+        df = DataFrame({'a' : [1, 2]})
+        result = df.get_dtype_counts()
+        expected = Series({'int64': 1 })
+        assert_series_equal(result, expected)
+
+        df = DataFrame({'a':[1,2,4,7], 'b':[1.2, 2.3, 5.1, 6.3], 
+                        'c':list('abcd'), 'd':[datetime(2000,1,1) for i in range(4)],
+                        'e' : [1.,2,4.,7]})
         result = df.get_dtype_counts()
-        # TODO: fix this on 32-bit (or decide it's ok behavior?)
-        # expected = Series({intname: 1, floatname : 1, datetime64name: 1, objectname : 1})
-        expected = Series({'int64': 1, floatname : 1, datetime64name: 1, objectname : 1})
+        expected = Series({'int64': 1, 'float64' : 2, datetime64name: 1, objectname : 1})
         result.sort()
         expected.sort()
         assert_series_equal(result, expected)