Support selection masks and expressions on gridded data (#4882)

Author: philippjfr

holoviews/core/data/grid.py

@@ -548,6 +548,9 @@ def key_select_mask(cls, dataset, values, ind):
 
     @classmethod
     def select(cls, dataset, selection_mask=None, **selection):
+        if selection_mask is not None:
+            raise ValueError("Masked selections currently not supported for {0}.".format(cls.__name__))
+
         dimensions = dataset.kdims
         val_dims = [vdim for vdim in dataset.vdims if vdim in selection]
         if val_dims:

holoviews/core/data/xarray.py

@@ -537,6 +537,9 @@ def mask(cls, dataset, mask, mask_val=np.nan):
 
     @classmethod
     def select(cls, dataset, selection_mask=None, **selection):
+        if selection_mask is not None:
+            return dataset.data.where(selection_mask, drop=True)
+
         validated = {}
         for k, v in selection.items():
             dim = dataset.get_dimension(k, strict=True)