Merge pull request #4038 from AaronStiff/3984-facets-empty-dataset

added: ignore facet args with empty dataset

Author: alexcjohnson

CHANGELOG.md

@@ -6,6 +6,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Fixed
   - Fixed another compatibility issue with Pandas 2.0, just affecting `px.*(line_close=True)` [[#4190](https://github.com/plotly/plotly.py/pull/4190)]
+  - Empty pandas dataframe with facet row/column set no longer fails [[#4038](https://github.com/plotly/plotly.py/pull/4038)]
   - Added some rounding to the `make_subplots` function to handle situations where the user-input specs cause the domain to exceed 1 by small amounts [[#4153](https://github.com/plotly/plotly.py/pull/4153)]
   - Sanitize JSON output to prevent an XSS vector when graphs are inserted directly into HTML [[#4196](https://github.com/plotly/plotly.py/pull/4196)]
   - Fixed issue with shapes and annotations plotting on the wrong y axis when supplied with a specific axis in the `yref` parameter [[#4177](https://github.com/plotly/plotly.py/pull/4177)]

packages/python/plotly/plotly/express/_core.py

@@ -1880,6 +1880,10 @@ def infer_config(args, constructor, trace_patch, layout_patch):
         args[position] = args["marginal"]
         args[other_position] = None
 
+    # Ignore facet rows and columns when data frame is empty so as to prevent nrows/ncols equaling 0
+    if len(args["data_frame"]) == 0:
+        args["facet_row"] = args["facet_col"] = None
+
     # If both marginals and faceting are specified, faceting wins
     if args.get("facet_col") is not None and args.get("marginal_y") is not None:
         args["marginal_y"] = None

test/percy/plotly-express.py

@@ -543,3 +543,6 @@
 )
 fig = px.timeline(df, x_start="Start", x_end="Finish", y="Task", color="Task")
 fig.write_html(os.path.join(dir_name, "timeline.html"), auto_play=False)
+
+
+px.bar(pd.DataFrame(columns=["A", "B", "X"]), x="A", y="X", facet_col="B")