Merge pull request #6728 from gerritholl/structured_multidim_masked_array_fillvalue

BUG/TST: Fix for #6723 including test: force fill_value.ndim==0

2 files changed, 24 insertions, 0 deletions

diff --git a/numpy/ma/core.py b/numpy/ma/core.py
index 9b0b1cc79..25b926e6b 100644
--- a/numpy/ma/core.py
+++ b/numpy/ma/core.py
@@ -3129,6 +3129,26 @@ class MaskedArray(ndarray):
             if isinstance(indx, basestring):
                 if self._fill_value is not None:
                     dout._fill_value = self._fill_value[indx]
+
+                    # If we're indexing a multidimensional field in a 
+                    # structured array (such as dtype("(2,)i2,(2,)i1")),
+                    # dimensionality goes up (M[field].ndim == M.ndim +
+                    # len(M.dtype[field].shape)).  That's fine for 
+                    # M[field] but problematic for M[field].fill_value 
+                    # which should have shape () to avoid breaking several
+                    # methods. There is no great way out, so set to
+                    # first element.  See issue #6723.
+                    if dout._fill_value.ndim > 0:
+                        if not (dout._fill_value ==
+                                dout._fill_value.flat[0]).all():
+                            warnings.warn(
+                                "Upon accessing multidimensional field "
+                                "{indx:s}, need to keep dimensionality "
+                                "of fill_value at 0. Discarding "
+                                "heterogeneous fill_value and setting "
+                                "all to {fv!s}.".format(indx=indx,
+                                    fv=dout._fill_value[0]))
+                        dout._fill_value = dout._fill_value.flat[0]
                 dout._isfield = True
             # Update the mask if needed
             if _mask is not nomask:
diff --git a/numpy/ma/tests/test_core.py b/numpy/ma/tests/test_core.py
index adbbb26d1..9e5ad51bd 100644
--- a/numpy/ma/tests/test_core.py
+++ b/numpy/ma/tests/test_core.py
@@ -1662,6 +1662,10 @@ class TestFillingValues(TestCase):
         assert_equal(test, control)
         control = np.array((0, 0, 0), dtype="int, float, float").astype(ndtype)
         assert_equal(_check_fill_value(0, ndtype), control)
+        # but when indexing, fill value should become scalar not tuple
+        # See issue #6723
+        M = masked_array(control)
+        assert_equal(M["f1"].fill_value.ndim, 0)
 
     def test_fillvalue_datetime_timedelta(self):
         # Test default fillvalue for datetime64 and timedelta64 types.