Merge pull request #3765 from plotly/one_group_short_circuit

PX: Avoid `groupby` when possible and access groups more efficiently

Author: nicolaskruchten

Diff for: CHANGELOG.md

@@ -10,6 +10,10 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   - `pattern_shape` options now available in `px.timeline()` [#3774](https://github.com/plotly/plotly.py/pull/3774)
   - `facet_*` and `category_orders` now available in `px.pie()` [#3775](https://github.com/plotly/plotly.py/pull/3775)
 
+### Performance
+
+  - `px` methods no longer call `groupby` on the input dataframe when the result would be a single group, and no longer groups by a lambda, for significant speedups [#3765](https://github.com/plotly/plotly.py/pull/3765)
+
 ### Updated
 
   - Allow non-string extras in `flaglist` attributes, to support upcoming changes to `ax.automargin` in plotly.js [plotly.js#6193](https://github.com/plotly/plotly.js/pull/6193), [#3749](https://github.com/plotly/plotly.py/pull/3749)

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

@@ -1920,40 +1920,66 @@ def infer_config(args, constructor, trace_patch, layout_patch):
     return trace_specs, grouped_mappings, sizeref, show_colorbar
 
 
-def get_orderings(args, grouper, grouped):
+def get_groups_and_orders(args, grouper):
     """
     `orders` is the user-supplied ordering with the remaining data-frame-supplied
     ordering appended if the column is used for grouping. It includes anything the user
     gave, for any variable, including values not present in the dataset. It's a dict
     where the keys are e.g. "x" or "color"
 
-    `sorted_group_names` is the set of groups, ordered by the order above. It's a list
-    of tuples like [("value1", ""), ("value2", "")] where each tuple contains the name
+    `groups` is the dicts of groups, ordered by the order above. Its keys are
+    tuples like [("value1", ""), ("value2", "")] where each tuple contains the name
     of a single dimension-group
     """
-
     orders = {} if "category_orders" not in args else args["category_orders"].copy()
+
+    # figure out orders and what the single group name would be if there were one
+    single_group_name = []
+    unique_cache = dict()
     for col in grouper:
-        if col != one_group:
-            uniques = list(args["data_frame"][col].unique())
+        if col == one_group:
+            single_group_name.append("")
+        else:
+            if col not in unique_cache:
+                unique_cache[col] = list(args["data_frame"][col].unique())
+            uniques = unique_cache[col]
+            if len(uniques) == 1:
+                single_group_name.append(uniques[0])
             if col not in orders:
                 orders[col] = uniques
             else:
                 orders[col] = list(OrderedDict.fromkeys(list(orders[col]) + uniques))
+    df = args["data_frame"]
+    if len(single_group_name) == len(grouper):
+        # we have a single group, so we can skip all group-by operations!
+        groups = {tuple(single_group_name): df}
+    else:
+        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(required_grouper) != 1 else (g,) for g in group_indices
+        ]
 
-    sorted_group_names = []
-    for group_name in grouped.groups:
-        if len(grouper) == 1:
-            group_name = (group_name,)
-        sorted_group_names.append(group_name)
-
-    for i, col in reversed(list(enumerate(grouper))):
-        if col != one_group:
+        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,
             )
-    return orders, sorted_group_names
+
+        # 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 = {
+            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
 
 
 def make_figure(args, constructor, trace_patch=None, layout_patch=None):
@@ -1974,9 +2000,7 @@ def make_figure(args, constructor, trace_patch=None, layout_patch=None):
         args, constructor, trace_patch, layout_patch
     )
     grouper = [x.grouper or one_group for x in grouped_mappings] or [one_group]
-    grouped = args["data_frame"].groupby(grouper, sort=False)
-
-    orders, sorted_group_names = get_orderings(args, grouper, grouped)
+    groups, orders = get_groups_and_orders(args, grouper)
 
     col_labels = []
     row_labels = []
@@ -2005,8 +2029,7 @@ def make_figure(args, constructor, trace_patch=None, layout_patch=None):
     trendline_rows = []
     trace_name_labels = None
     facet_col_wrap = args.get("facet_col_wrap", 0)
-    for group_name in sorted_group_names:
-        group = grouped.get_group(group_name if len(group_name) > 1 else group_name[0])
+    for group_name, group in groups.items():
         mapping_labels = OrderedDict()
         trace_name_labels = OrderedDict()
         frame_name = ""
@@ -2224,6 +2247,8 @@ def make_figure(args, constructor, trace_patch=None, layout_patch=None):
     fig.update_layout(layout_patch)
     if "template" in args and args["template"] is not None:
         fig.update_layout(template=args["template"], overwrite=True)
+    for f in frame_list:
+        f["name"] = str(f["name"])
     fig.frames = frame_list if len(frames) > 1 else []
 
     if args.get("trendline") and args.get("trendline_scope", "trace") == "overall":