BUG: Handle overlapping line and bar on the same plot #61173

MartinBraquet · 2025-03-24T09:22:19Z

closes BUG: fails to plot 2 plots with secondary y axis when index type is PeriodIndex and plot kinds are different #61161
Tests added and passed if fixing a bug or adding a new feature
All code checks passed.
Added type annotations to new arguments/methods/functions.
Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

This code

import pandas as pd
import matplotlib.pyplot as plt

index = pd.period_range('2023', periods=3, freq='Y')
df = pd.DataFrame({
    'col1': [10, 20, 30],
    'col2': [40, 25, 10]
}, index=index)

fig, ax = plt.subplots()
df['col1'].plot(kind='bar', ax=ax)
ax2 = ax.twinx()
df['col2'].plot(kind='line', ax=ax2, color = 'r')
plt.show()

from the linked issue gives this plot:

And swapping the lines (line before bar)

df['col2'].plot(kind='line', ax=ax2, color = 'r')
df['col1'].plot(kind='bar', ax=ax)

gives

I believe the difference of results stems from the fact that the figure is always cropped to match the x-range of the last plot. We can certainly adjust the PR to make the first figure behave like the second one if desired.

Please provide feedback on the overall approach. Once confirmed, I'll expand and cover with tests.

rhshadrach

Thanks for the PR! Can you add a test in pandas/tests/plotting/test_series.py. Make the plots and check that the x-axis is as expected.

rhshadrach · 2025-03-26T14:21:08Z

pandas/plotting/_matplotlib/core.py

@@ -1868,6 +1870,14 @@ def __init__(

        MPLPlot.__init__(self, data, **kwargs)

+        if isinstance(data.index, ABCPeriodIndex):
+            self.ax.freq = data.index.freq


Why is the modification of freq necessary? I worry that we don't own ax, and that we shouldn't be mutating it. But I'm not too familiar with the plotting code; do we do this anywhere else? I don't see any instances at a glance.

The only reason is to pass the freq to PeriodConverter, which currently only accepts ax as input arg, not freq. It can obviously be made cleaner. I meant to modify PeriodConverter or find a cleaner way than hacking around ax.

I'd just like to get a thorough review of the overall approach, i.e. shifting the tick positions, as it would apply to all box plots with PeriodIndex, and hence is a potential major change. Not sure how well it is covered by tests currently; I don't want to insert regressions or breaking changes. It would be good to have it first checked by a maintainer well-versed with matplotlib, as I'm not so familiar with all the idiosyncrasies of the ax object.

Introduce `convert_from_freq` method and streamline the conversion process by passing `freq` directly instead of using `axis.freq`. This improves modularity and ensures clearer separation of concerns for frequency handling in Period conversion.

Simplified `tick_pos` calculation by reusing helper methods and added a decorator to register pandas Matplotlib converters in the `_plot` method. This improves clarity and ensures proper integration with the pandas Matplotlib ecosystem.

This test ensures that bar and line plots with identical x values are correctly superposed on the same axes. It verifies that the x-tick positions remain consistent across plot types.

MartinBraquet · 2025-04-07T15:48:58Z

pandas/tests/plotting/test_series.py

@@ -971,3 +971,17 @@ def test_secondary_y_subplot_axis_labels(self):
        s1.plot(ax=ax2)
        assert len(ax.xaxis.get_minor_ticks()) == 0
        assert len(ax.get_xticklabels()) > 0
+
+    def test_bar_line_plot(self):


Fails on main

Resolved a bug that prevented a line and bar from aligning on the same plot in `Series.plot`. This addresses issue pandas-dev#61161 and improves plot consistency when combining these chart types.

Move `x_compat` logic and time series helper methods from `LinePlot` to `MPLPlot` for better reusability and maintainability. This simplifies the `LinePlot` class and centralizes common functionality.

MartinBraquet · 2025-04-07T16:25:22Z

pandas/plotting/_matplotlib/converter.py

+        return PeriodConverter.convert_from_freq(values, axis.freq)
+
+    @staticmethod
+    def convert_from_freq(values, freq):


convert only uses the freq attribute of axis, so one should allow the user to pass freq without axis object.

MartinBraquet · 2025-04-07T16:27:09Z

pandas/plotting/_matplotlib/core.py

+        from pandas.plotting import plot_params
+
+        self.x_compat = plot_params["x_compat"]
+        if "x_compat" in self.kwds:
+            self.x_compat = bool(self.kwds.pop("x_compat"))
+
+    @final
+    def _is_ts_plot(self) -> bool:
+        # this is slightly deceptive
+        return not self.x_compat and self.use_index and self._use_dynamic_x()
+
+    @final
+    def _use_dynamic_x(self) -> bool:
+        return use_dynamic_x(self._get_ax(0), self.data)
+


Those routines are not exclusive to LinePlot, as they seem related to any type of time series. _is_ts_plot is used in this PR to check if a boxplot is a time series.

MartinBraquet · 2025-04-07T16:28:18Z

@rhshadrach I covered the change with a test. I believe the PR is now ready for review and then merge.

Handle line and box on the same plot

3caf8e6

MartinBraquet changed the title ~~BUG: Handle line and box on the same plot~~ BUG: Handle line and bar on the same plot Mar 24, 2025

MartinBraquet mentioned this pull request Mar 24, 2025

BUG: fails to plot 2 plots with secondary y axis when index type is PeriodIndex and plot kinds are different #61161

Open

3 tasks

Handle line and box on the same plot

97d0440

rhshadrach requested changes Mar 26, 2025

View reviewed changes

rhshadrach added Bug Visualization plotting labels Mar 26, 2025

MartinBraquet added 3 commits April 7, 2025 22:34

Add test for bar and line plot superposition with same x values

e5b4e6f

This test ensures that bar and line plots with identical x values are correctly superposed on the same axes. It verifies that the x-tick positions remain consistent across plot types.

MartinBraquet commented Apr 7, 2025

View reviewed changes

MartinBraquet changed the title ~~BUG: Handle line and bar on the same plot~~ BUG: Handle overlapping line and bar on the same plot Apr 7, 2025

MartinBraquet added 3 commits April 7, 2025 22:56

Merge branch 'main' into plot

c5a6554

Fix alignment issue in Series.plot with line and bar.

218871d

Resolved a bug that prevented a line and bar from aligning on the same plot in `Series.plot`. This addresses issue pandas-dev#61161 and improves plot consistency when combining these chart types.

Refactor time series handling in matplotlib plotting.

16762b6

Move `x_compat` logic and time series helper methods from `LinePlot` to `MPLPlot` for better reusability and maintainability. This simplifies the `LinePlot` class and centralizes common functionality.

MartinBraquet commented Apr 7, 2025

View reviewed changes

MartinBraquet mentioned this pull request Apr 7, 2025

BUG: Handle overlapping line and scatter on the same plot #61244

Open

5 tasks

Merge branch 'main' into plot

bb2fdd7

MartinBraquet requested a review from rhshadrach April 8, 2025 04:29

Merge branch 'main' into plot

950441b

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BUG: Handle overlapping line and bar on the same plot #61173

BUG: Handle overlapping line and bar on the same plot #61173

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BUG: Handle overlapping line and bar on the same plot #61173

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