Fix Express legend groups with duplicate labels

CHANGELOG.md

@@ -8,6 +8,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Add support for converting matplotlib reference lines (`axhline`, `axvline`, and horizontal/vertical `axline`) as well as axes-coordinate lines into Plotly layout shapes in `mpl_to_plotly`, including support for date axes [[#5719](https://github.com/plotly/plotly.py/pull/5719)], with thanks to @robertoffmoura for the contribution!
 
 ### Fixed
+- Preserve distinct Plotly Express legend entries and groups when grouping columns have the same display label ([#2562](https://github.com/plotly/plotly.py/issues/2562)).
 - Fix `mpl_to_plotly` tick marker mirroring, axis positioning, and trace visibility for twinned and overlaid subplots (such as `twinx` and `twiny`) [[#5310](https://github.com/plotly/plotly.py/pull/5310)], with thanks to @robertoffmoura for the contribution!
 - Fix `mpl_to_plotly` losing matplotlib axis line colors by exporting the color of each axis's displayed spine to the plotly x and y axis `linecolor` [[#5311](https://github.com/plotly/plotly.py/pull/5311)], with thanks to @robertoffmoura for the contribution!
 - Fix concurrent first access to lazily initialized graph object properties, which could raise `ValueError("Invalid value")` [[#5691](https://github.com/plotly/plotly.py/pull/5691)], with thanks to @hb1915 for the contribution!

plotly/express/_core.py

@@ -2594,7 +2594,7 @@ def make_figure(args, constructor, trace_patch=None, layout_patch=None):
                 if not isinstance(m.val_map, IdentityMap):
                     mapping_labels[key] = str(val)
                     if m.show_in_trace_name:
-                        trace_name_labels[key] = str(val)
+                        trace_name_labels[col] = str(val)
                 if m.variable == "animation_frame":
                     frame_name = val
         trace_name = ", ".join(trace_name_labels.values())
@@ -2768,7 +2768,9 @@ def make_figure(args, constructor, trace_patch=None, layout_patch=None):
             layout_patch[v] = args[v]
     layout_patch["legend"] = dict(tracegroupgap=0)
     if trace_name_labels:
-        layout_patch["legend"]["title_text"] = ", ".join(trace_name_labels)
+        layout_patch["legend"]["title_text"] = ", ".join(
+            get_label(args, column) for column in trace_name_labels
+        )
     if args["title"]:
         layout_patch["title_text"] = args["title"]
     elif args["template"].layout.margin.t is None:

tests/test_optional/test_px/test_px.py

@@ -92,6 +92,41 @@ def test_labels(backend):
     assert fig.layout.annotations[4].text.startswith("TIME")
 
 
+@pytest.mark.parametrize(
+    "labels", [{"color": "Group", "symbol": "Group"}, {"color": "symbol"}]
+)
+def test_legend_with_duplicate_labels(constructor, labels):
+    df = constructor(
+        {
+            "x": [1, 2, 3, 4],
+            "y": [4, 3, 2, 1],
+            "color": ["A", "A", "B", "B"],
+            "symbol": ["one", "two", "one", "two"],
+        }
+    )
+    fig = px.scatter(df, x="x", y="y", color="color", symbol="symbol", labels=labels)
+
+    expected_names = ["A, one", "A, two", "B, one", "B, two"]
+    assert [trace.name for trace in fig.data] == expected_names
+    assert [trace.legendgroup for trace in fig.data] == expected_names
+    assert all(trace.showlegend for trace in fig.data)
+    assert fig.layout.legend.title.text == ", ".join(
+        labels.get(column, column) for column in ["color", "symbol"]
+    )
+
+
+def test_legend_with_same_column_for_color_and_symbol(constructor):
+    df = constructor({"x": [1, 2], "y": [3, 4], "group": ["A", "B"]})
+    fig = px.scatter(
+        df, x="x", y="y", color="group", symbol="group", labels={"group": "Group"}
+    )
+
+    assert [trace.name for trace in fig.data] == ["A", "B"]
+    assert [trace.legendgroup for trace in fig.data] == ["A", "B"]
+    assert all(trace.showlegend for trace in fig.data)
+    assert fig.layout.legend.title.text == "Group"
+
+
 @pytest.mark.parametrize(
     ["extra_kwargs", "expected_mode"],
     [