BUG: Make transpose and diagonal masks be views

Fixes gh-8506 and fixes gh-7483

2 files changed, 24 insertions, 4 deletions

diff --git a/numpy/ma/core.py b/numpy/ma/core.py
index deddacfdc..0035cd9f7 100644
--- a/numpy/ma/core.py
+++ b/numpy/ma/core.py
@@ -2558,7 +2558,8 @@ def _arraymethod(funcname, onmask=True):
         if not onmask:
             result.__setmask__(mask)
         elif mask is not nomask:
-            result.__setmask__(getattr(mask, funcname)(*args, **params))
+            # __setmask__ makes a copy, which we don't want
+            result._mask = getattr(mask, funcname)(*args, **params)
         return result
     methdoc = getattr(ndarray, funcname, None) or getattr(np, funcname, None)
     if methdoc is not None:
diff --git a/numpy/ma/tests/test_core.py b/numpy/ma/tests/test_core.py
index e3c35cf81..b19a138ab 100644
--- a/numpy/ma/tests/test_core.py
+++ b/numpy/ma/tests/test_core.py
@@ -3205,9 +3205,7 @@ class TestMaskedArrayMethods(object):
         assert_(m_arr_sq is not np.ma.masked)
         assert_equal(m_arr_sq.mask, True)
         m_arr_sq[...] = 2
-        # TODO: mask isn't copied to/from views yet in maskedarray, so we can
-        #       only check the data
-        assert_equal(m_arr.data[0,0], 2)
+        assert_equal(m_arr[0,0], 2)
 
     def test_swapaxes(self):
         # Tests swapaxes on MaskedArrays.
@@ -3396,6 +3394,27 @@ class TestMaskedArrayMethods(object):
         assert_equal(x.T.mask, x.mask)
         assert_equal(x.T.data, x.data)
 
+    def test_transpose_view(self):
+        x = np.ma.array([[1, 2, 3], [4, 5, 6]])
+        x[0,1] = np.ma.masked
+        xt = x.T
+
+        xt[1,0] = 10
+        xt[0,1] = np.ma.masked
+
+        assert_equal(x.data, xt.T.data)
+        assert_equal(x.mask, xt.T.mask)
+
+    def test_diagonal_view(self):
+        x = np.ma.zeros((3,3))
+        x[0,0] = 10
+        x[1,1] = np.ma.masked
+        x[2,2] = 20
+        xd = x.diagonal()
+        x[1,1] = 15
+        assert_equal(xd.mask, x.diagonal().mask)
+        assert_equal(xd.data, x.diagonal().data)
+
 
 class TestMaskedArrayMathMethods(object):