[NumPy-Tickets] [NumPy] #1751: recfunctions.append_fields fails on arrays containing objects

[NumPy Trac]

#1751: recfunctions.append_fields fails on arrays containing objects
---------------------+------------------------------------------------------
 Reporter:  aickley  |       Owner:  somebody
     Type:  defect   |      Status:  new     
 Priority:  normal   |   Milestone:  2.0.0   
Component:  Other    |     Version:  1.5.1   
 Keywords:           |  
---------------------+------------------------------------------------------
 The problem is that append_fields calls array.view() which does not accept
 arrays containing objects (See
 [http://projects.scipy.org/numpy/ticket/674])

 Test case (to include in numpy/lib/tests/recfunctions.py):
 {{{
 class TestAppendFieldsObj(TestCase):
     """
     Test append_fields with arrays containing objects
     """
     def setUp(self):
         from datetime import date
         self.data = dict(obj=date(2000, 1, 1))

     def test_append_to_objects(self):
         "Test append_fields when the base array contains objects"
         obj = self.data['obj']
         x = np.array([(obj, 1.), (obj, 2.)], dtype=[('A', object), ('B',
 float)])
         y = np.array([10, 20], dtype=int)
         test = append_fields(x, 'C', data=y, usemask=False)
         control = np.array([(obj, 1.0, 10), (obj, 2.0, 20)],
                            dtype=[('A', object), ('B', float), ('C',
 int)])
         assert_equal(test, control)
     #
     def test_append_with_objects(self):
         "Test append_fields when the appended data contains objects"
         obj = self.data['obj']
         x = np.array([(10, 1.), (20, 2.)], dtype=[('A', int), ('B',
 float)])
         y = np.array([obj, obj], dtype=object)
         test = append_fields(y, 'C', data=y, dtypes=object, usemask=False)
         control = np.array([(10, 1.0, obj), (20, 2.0, obj)],
                            dtype=[('A', int), ('B', float), ('C',
 object)])
         assert_equal(test, control)

 }}}

 {{{
 ======================================================================
 ERROR: Test append_fields when the base array contains objects
 ----------------------------------------------------------------------
 Traceback (most recent call last):
   File "/home/kolpakov/lib/python2.6/site-
 packages/numpy/lib/tests/test_recfunctions.py", line 406, in
 test_append_to_objects
     test = append_fields(x, 'C', data=y, usemask=False)
   File "/home/kolpakov/lib/python2.6/site-
 packages/numpy/lib/recfunctions.py", line 629, in append_fields
     base = merge_arrays(base, usemask=usemask, fill_value=fill_value)
   File "/home/kolpakov/lib/python2.6/site-
 packages/numpy/lib/recfunctions.py", line 399, in merge_arrays
     return seqarrays.view(dtype=seqdtype, type=seqtype)
 TypeError: Cannot change data-type for object array.

 ======================================================================
 ERROR: Test append_fields when the appended data contains objects
 ----------------------------------------------------------------------
 Traceback (most recent call last):
   File "/home/kolpakov/lib/python2.6/site-
 packages/numpy/lib/tests/test_recfunctions.py", line 416, in
 test_append_with_objects
     test = append_fields(y, 'C', data=y, dtypes=object, usemask=False)
   File "/home/kolpakov/lib/python2.6/site-
 packages/numpy/lib/recfunctions.py", line 627, in append_fields
     for (a, n, d) in zip(data, names, dtypes)]
 TypeError: Cannot change data-type for object array.

 ----------------------------------------------------------------------
 Ran 33 tests in 0.062s
 }}}

 Regarding the first failure, append_fields calls merge_arrays on the base
 array:
 {{{
 base = merge_arrays(base, usemask=usemask, fill_value=fill_value)
 }}}.
 Actually this line can be completely removed without breaking existing
 unit tests. I don't like this call because if we are calling merge_array
 on a single array we are are not actually _merging_ anything, but rather
 making sure that the array conforms to certain criteria. Maybe this code
 should be refactored out from merge_arrays...

-- 
Ticket URL: <http://projects.scipy.org/numpy/ticket/1751>
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