Fix: Add defensive check for empty column_ids in unpivot function

shuoweil · shuoweil · commit 9485b00833c0 · 2026-01-07T05:58:04.000Z
diff --git a/bigframes/core/blocks.py b/bigframes/core/blocks.py
@@ -3433,6 +3433,9 @@ def unpivot(
         )
     new_passthrough_cols = [column_mapping[col] for col in passthrough_columns]
     # Last column is offsets
+    if not labels_array.column_ids:
+        # Handle empty column_ids case for multimodal DataFrames
+        return array_value, (tuple(), tuple(), tuple(passthrough_columns))
     index_col_ids = [labels_mapping[col] for col in labels_array.column_ids[:-1]]
     explode_offsets_id = labels_mapping[labels_array.column_ids[-1]]
 

Original file line number	Diff line number	Diff line change
`@@ -3433,6 +3433,9 @@ def unpivot(`
`3433`	`3433`	`)`
`3434`	`3434`	`new_passthrough_cols = [column_mapping[col] for col in passthrough_columns]`
`3435`	`3435`	`# Last column is offsets`
	`3436`	`+ if not labels_array.column_ids:`
	`3437`	`+ # Handle empty column_ids case for multimodal DataFrames`
	`3438`	`+ return array_value, (tuple(), tuple(), tuple(passthrough_columns))`
`3436`	`3439`	`index_col_ids = [labels_mapping[col] for col in labels_array.column_ids[:-1]]`
`3437`	`3440`	`explode_offsets_id = labels_mapping[labels_array.column_ids[-1]]`
`3438`	`3441`