🧹 avoid unnecessary one_group groupby operations

Author: jvdd

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

@@ -1938,21 +1938,30 @@ def get_groups_and_orders(args, grouper):
         # we have a single group, so we can skip all group-by operations!
         groups = {tuple(single_group_name): df}
     else:
-        grouped = df.groupby(grouper, sort=False)
+        required_grouper = [g for g in grouper if g != one_group]
+        grouped = df.groupby(required_grouper, sort=False)  # skip one_group groupers
         group_indices = grouped.indices
-        sorted_group_names = [g if len(grouper) != 1 else (g,) for g in group_indices]
+        sorted_group_names = [
+            g if len(required_grouper) != 1 else (g,) for g in group_indices
+        ]
 
-        for i, col in reversed(list(enumerate(grouper))):
-            if col != one_group:
-                sorted_group_names = sorted(
-                    sorted_group_names,
-                    key=lambda g: orders[col].index(g[i])
-                    if g[i] in orders[col]
-                    else -1,
-                )
+        for i, col in reversed(list(enumerate(required_grouper))):
+            sorted_group_names = sorted(
+                sorted_group_names,
+                key=lambda g: orders[col].index(g[i]) if g[i] in orders[col] else -1,
+            )
+
+        # calculate the full group_names by inserting "" in the tuple index for one_group groups
+        full_sorted_group_names = [list(t) for t in sorted_group_names]
+        for i, col in enumerate(grouper):
+            if col == one_group:
+                for g in full_sorted_group_names:
+                    g.insert(i, "")
+        full_sorted_group_names = [tuple(g) for g in full_sorted_group_names]
 
         groups = {
-            s: grouped.get_group(s if len(s) > 1 else s[0]) for s in sorted_group_names
+            sf: grouped.get_group(s if len(s) > 1 else s[0])
+            for sf, s in zip(full_sorted_group_names, sorted_group_names)
         }
     return groups, orders