BUG: Fix inconsistency between the shape properties of SparseSeries and SparseArray (pandas-dev#21126)

Author: nprad

pandas/core/sparse/array.py

@@ -290,7 +290,9 @@ def __reduce__(self):
         """Necessary for making this object picklable"""
         object_state = list(np.ndarray.__reduce__(self))
         subclass_state = self.fill_value, self.sp_index
-        object_state[2] = (object_state[2], subclass_state)
+        object_state[2] = list(object_state[2])
+        object_state[2][1] = super(SparseArray, self).shape
+        object_state[2] = (tuple(object_state[2]), subclass_state)
         return tuple(object_state)
 
     def __setstate__(self, state):
@@ -339,6 +341,10 @@ def values(self):
         output.put(int_index.indices, self)
         return output
 
+    @property
+    def shape(self):
+        return (len(self),)
+
     @property
     def sp_values(self):
         # caching not an option, leaks memory

pandas/tests/sparse/test_array.py

@@ -454,6 +454,16 @@ def test_values_asarray(self):
         assert_almost_equal(self.arr.to_dense(), self.arr_data)
         assert_almost_equal(self.arr.sp_values, np.asarray(self.arr))
 
+    def test_shape(self):
+        out = SparseArray([0, 0, 0, 0, 0])
+        assert out.shape == (5,)
+
+        out = SparseArray([])
+        assert out.shape == (0,)
+
+        out = SparseArray([0])
+        assert out.shape == (1,)
+
     def test_to_dense(self):
         vals = np.array([1, np.nan, np.nan, 3, np.nan])
         res = SparseArray(vals).to_dense()