Make facet error more informative (#3264)

vega · Nov 14, 2023 · bf52ed1 · bf52ed1
1 parent 6cc31d6
commit bf52ed1
Showing 1 changed file with 4 additions and 1 deletion.
diff --git a/altair/vegalite/v5/api.py b/altair/vegalite/v5/api.py
@@ -2766,7 +2766,10 @@ def facet(
             # Remove "ignore" statement once Undefined is no longer typed as Any
             if self.data is Undefined:  # type: ignore
                 raise ValueError(
-                    "Facet charts require data to be specified at the top level."
+                    "Facet charts require data to be specified at the top level. "
+                    "If you are trying to facet layered or concatenated charts, "
+                    "ensure that the same data variable is passed to each chart "
+                    "or specify the data inside the facet method instead."
                 )
             # ignore type as copy comes from another class
             self = self.copy(deep=False)  # type: ignore[attr-defined]