More flexible parallel_categories magic

Author: nicolaskruchten

Diff for: packages/python/plotly/plotly/express/_chart_types.py

@@ -1205,6 +1205,7 @@ def parallel_categories(
     template=None,
     width=None,
     height=None,
+    dimensions_max_cardinality=50,
 ):
     """
     In a parallel categories (or parallel sets) plot, each row of

Diff for: packages/python/plotly/plotly/express/_core.py

@@ -181,7 +181,9 @@ def make_trace_kwargs(args, trace_spec, g, mapping_labels, sizeref):
                 )
                 and (
                     trace_spec.constructor != go.Parcats
-                    or len(args["data_frame"][name].unique()) <= 20
+                    or (v is not None and name in v)
+                    or len(args["data_frame"][name].unique())
+                    <= args["dimensions_max_cardinality"]
                 )
             ]
             result["dimensions"] = [

Diff for: packages/python/plotly/plotly/express/_doc.py

@@ -106,6 +106,11 @@
         colref_list_desc,
         "Values from these columns are used for multidimensional visualization.",
     ],
+    dimensions_max_cardinality=[
+        "int (default 50)",
+        "When `dimensions` is `None` and `data_frame` is provided, "
+        "columns with more than this number of unique values are excluded from the output.",
+    ],
     error_x=[
         colref_type,
         colref_desc,