Implement MultiInterface.assign (#4880)

Author: philippjfr

holoviews/core/data/multipath.py

@@ -131,6 +131,16 @@ def _inner_dataset_template(cls, dataset, validate_vdims=True):
                        kdims=dataset.kdims, vdims=vdims,
                        _validate_vdims=validate_vdims)
 
+    @classmethod
+    def assign(cls, dataset, new_data):
+        ds = cls._inner_dataset_template(dataset)
+        assigned = []
+        for i, d in enumerate(dataset.data):
+            ds.data = d
+            new = ds.interface.assign(ds, {k: v[i:i+1] for k, v in new_data.items()})
+            assigned.append(new)
+        return assigned
+
     @classmethod
     def dimension_type(cls, dataset, dim):
         if not dataset.data: