diff --git a/hypernets_processor/data_io/dataset_util.py b/hypernets_processor/data_io/dataset_util.py
index 126f2a09..0159f798 100644
--- a/hypernets_processor/data_io/dataset_util.py
+++ b/hypernets_processor/data_io/dataset_util.py
@@ -53,6 +53,8 @@ def create_default_array(dim_sizes, dtype, dim_names=None, fill_value=None):
 
         if dim_names is not None:
             default_array = DataArray(empty_array, dims=dim_names)
+        elif (dim_names is None) and (dim_sizes == []):
+            default_array = DataArray(empty_array)
         else:
             default_array = DataArray(empty_array, dims=DEFAULT_DIM_NAMES[-len(dim_sizes):])
 
@@ -259,6 +261,50 @@ def unpack_flags(da):
 
         return ds
 
+    @staticmethod
+    def get_flags_mask_or(da, flags=None):
+        """
+        Returns boolean mask for set of flags, defined as logical or of flags
+
+        :type da: xarray.DataArray
+        :param da: dataset
+
+        :type flags: list
+        :param flags: list of flags (if unset all data flags selected)
+
+        :return: flag masks
+        :rtype: numpy.ndarray
+        """
+
+        flags_ds = DatasetUtil.unpack_flags(da)
+
+        flags = flags if flags is not None else flags_ds.variables
+        mask_flags = [flags_ds[flag].values for flag in flags]
+
+        return np.logical_or.reduce(mask_flags)
+
+    @staticmethod
+    def get_flags_mask_and(da, flags=None):
+        """
+        Returns boolean mask for set of flags, defined as logical and of flags
+
+        :type da: xarray.DataArray
+        :param da: dataset
+
+        :type flags: list
+        :param flags: list of flags (if unset all data flags selected)
+
+        :return: flag masks
+        :rtype: numpy.ndarray
+        """
+
+        flags_ds = DatasetUtil.unpack_flags(da)
+
+        flags = flags if flags is not None else flags_ds.variables
+        mask_flags = [flags_ds[flag].values for flag in flags]
+
+        return np.logical_and.reduce(mask_flags)
+
     @staticmethod
     def set_flag(da, flag_name, error_if_set=False):
         """
@@ -281,7 +327,9 @@ def set_flag(da, flag_name, error_if_set=False):
         flag_bit = flag_meanings.index(flag_name)
         flag_mask = flag_masks[flag_bit]
 
-        return da | flag_mask
+        da.values = da.values | flag_mask
+
+        return da
 
     @staticmethod
     def unset_flag(da, flag_name, error_if_unset=False):
@@ -305,7 +353,9 @@ def unset_flag(da, flag_name, error_if_unset=False):
         flag_bit = flag_meanings.index(flag_name)
         flag_mask = flag_masks[flag_bit]
 
-        return da & ~flag_mask
+        da.values = da.values & ~flag_mask
+
+        return da
 
     @staticmethod
     def get_set_flags(da):
diff --git a/hypernets_processor/data_io/tests/test_dataset_util.py b/hypernets_processor/data_io/tests/test_dataset_util.py
index 23b43a38..a82ca198 100644
--- a/hypernets_processor/data_io/tests/test_dataset_util.py
+++ b/hypernets_processor/data_io/tests/test_dataset_util.py
@@ -288,6 +288,62 @@ def test_unpack_flags(self):
         self.assertTrue((flags["flag7"].data == empty).all())
         self.assertTrue((flags["flag8"].data == empty).all())
 
+    def test_get_flags_mask_or(self):
+
+        ds = Dataset()
+        meanings = ["flag1", "flag2", "flag3", "flag4", "flag5", "flag6", "flag7", "flag8"]
+        flags_vector_variable = DatasetUtil.create_flags_variable([2,3], meanings, dim_names=["dim1", "dim2"],
+                                                                  attributes={"standard_name": "std"})
+
+        ds["flags"] = flags_vector_variable
+        ds["flags"] = DatasetUtil.set_flag(ds["flags"], "flag4")
+        ds["flags"][0, 1] = DatasetUtil.set_flag(ds["flags"][0, 1], "flag5")
+        ds["flags"][1, 1] = DatasetUtil.set_flag(ds["flags"][1, 1], "flag2")
+        ds["flags"][1, 2] = DatasetUtil.set_flag(ds["flags"][1, 2], "flag7")
+
+        flags_mask = DatasetUtil.get_flags_mask_or(ds["flags"], flags=["flag5", "flag2", "flag7"])
+
+        expected_flags_mask = np.array([[False, True, False], [False, True, True]], dtype=bool)
+
+        np.testing.assert_array_almost_equal(flags_mask, expected_flags_mask)
+
+    def test_get_flags_mask_all(self):
+        ds = Dataset()
+        meanings = ["flag1", "flag2", "flag3", "flag4", "flag5", "flag6", "flag7", "flag8"]
+        flags_vector_variable = DatasetUtil.create_flags_variable([2, 3], meanings, dim_names=["dim1", "dim2"],
+                                                                  attributes={"standard_name": "std"})
+
+        ds["flags"] = flags_vector_variable
+        ds["flags"] = DatasetUtil.set_flag(ds["flags"], "flag4")
+        ds["flags"][0, 1] = DatasetUtil.set_flag(ds["flags"][0, 1], "flag5")
+        ds["flags"][1, 1] = DatasetUtil.set_flag(ds["flags"][1, 1], "flag2")
+        ds["flags"][1, 2] = DatasetUtil.set_flag(ds["flags"][1, 2], "flag7")
+
+        flags_mask = DatasetUtil.get_flags_mask_or(ds["flags"])
+
+        expected_flags_mask = np.array([[True, True, True], [True, True, True]], dtype=bool)
+
+        np.testing.assert_array_almost_equal(flags_mask, expected_flags_mask)
+
+    def test_get_flags_mask_and(self):
+
+        ds = Dataset()
+        meanings = ["flag1", "flag2", "flag3", "flag4", "flag5", "flag6", "flag7", "flag8"]
+        flags_vector_variable = DatasetUtil.create_flags_variable([2,3], meanings, dim_names=["dim1", "dim2"],
+                                                                  attributes={"standard_name": "std"})
+
+        ds["flags"] = flags_vector_variable
+        ds["flags"] = DatasetUtil.set_flag(ds["flags"], "flag4")
+        ds["flags"][0, 1] = DatasetUtil.set_flag(ds["flags"][0, 1], "flag5")
+        ds["flags"][1, 1] = DatasetUtil.set_flag(ds["flags"][1, 1], "flag2")
+        ds["flags"][1, 1] = DatasetUtil.set_flag(ds["flags"][1, 1], "flag7")
+
+        flags_mask = DatasetUtil.get_flags_mask_and(ds["flags"], flags=["flag2", "flag7"])
+
+        expected_flags_mask = np.array([[False, False, False], [False, True, False]], dtype=bool)
+
+        np.testing.assert_array_almost_equal(flags_mask, expected_flags_mask)
+
     def test_get_set_flags(self):
 
         ds = Dataset()