BUG: Override SparseBlock._try_coerce_result to make result flatten and sparse

Author: Licht-T

pandas/core/internals.py

@@ -2855,6 +2855,12 @@ def sparse_reindex(self, new_index):
         return self.make_block_same_class(values, sparse_index=new_index,
                                           placement=self.mgr_locs)
 
+    def _try_coerce_result(self, result):
+        """ reverse of try_coerce_args """
+        if isinstance(result, np.ndarray):
+            result = SparseArray(result.flatten(), kind=self.kind)
+        return result
+
 
 def make_block(values, placement, klass=None, ndim=None, dtype=None,
                fastpath=False, **kwargs):