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.

doc/source/whatsnew/v3.0.0.rst

rhshadrach · 2025-04-13T17:33:21Z

pandas/tests/plotting/test_series.py

+        s.plot(kind="bar", ax=ax)
+        bar_xticks = ax.get_xticks().tolist()
+        s.plot(kind="line", ax=ax, color="r")
+        line_xticks = ax.get_xticks()[: len(s)].tolist()


I'm seeing ax.get_xticks() here have the same length as s; why have [: len(s)] here?

After plotting the line, the ticks change on my machine:

ax.get_xticks() Out[1]: array([53, 54, 55, 56]) ax.get_xticklabels() Out[2]: [Text(53, 0, '2023'), Text(54, 0, '2024'), Text(55, 0, '2025'), Text(56, 0, '2026')]

A fourth tick is added by matplotlib for '2026'.

Even for integer indices, matplotlib does not do a 1-to-1 mapping between each x-tick and data point, as attested below:

ax = plt.subplot() plt.plot(s.values, [1, 2,3]) ax.get_xticks()

array([0.75, 1. , 1.25, 1.5 , 1.75, 2. , 2.25, 2.5 , 2.75, 3. , 3.25])

Not sure if you can reproduce those results on your machine, but I think that the exact number of ticks is irrelevant. I would suggest that this test checks that both x-tick labels (after bar plot and after line plot) include at least the 3 three ticks in the index (2023, 2024, 2025) and that the associated x-tick positions are the same for both plots. This would ensure that the two plots are superposed.
Additionally, the test can check that x-lim includes those three x-tick positions, which would ensure that the current plot view render the two plots.

I added a commit to reflect what I said above. Happy to discuss or update the code further if there is a need.

# Conflicts: # doc/source/whatsnew/v3.0.0.rst # pandas/plotting/_matplotlib/core.py

Ensure bar and line plots share consistent x-axis tick labels and verify that x-axis limits are adjusted to make all plotted elements visible in `test_bar_line_plot` test. These changes improve the robustness of visual alignment and boundary checks.

Add an assertion to verify the length of `bar_xticks` aligns with the length of the index. This improves the test's robustness by ensuring the data and ticks remain consistent.

MartinBraquet · 2025-04-14T04:37:31Z

pandas/tests/plotting/test_series.py

+        assert len(bar_xticks) == len(index)
+        assert bar_xticks == line_xticks


This is checking that

the three index years are in the two plots

the x-tick positions for those years are the same in the two plots

MartinBraquet · 2025-04-14T04:38:44Z

pandas/tests/plotting/test_series.py

+        assert x_limits[0] <= bar_xticks[0].get_position()[0]
+        assert x_limits[1] >= bar_xticks[-1].get_position()[0]


Check that both left-most and right-most data points are shown in the current view

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

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Handle line and box on the same plot

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rhshadrach requested changes Mar 26, 2025

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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

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MartinBraquet mentioned this pull request Apr 7, 2025

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

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Merge branch 'main' into plot

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

MartinBraquet added 2 commits April 8, 2025 11:29

Merge branch 'main' into plot

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Merge branch 'main' into plot

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# Conflicts: # doc/source/whatsnew/v3.0.0.rst # pandas/plotting/_matplotlib/core.py

MartinBraquet added 3 commits April 14, 2025 11:18

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Ensure bar_xticks length matches index in test_series.py

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Add an assertion to verify the length of `bar_xticks` aligns with the length of the index. This improves the test's robustness by ensuring the data and ticks remain consistent.

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

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		assert len(bar_xticks) == len(index)
		assert bar_xticks == line_xticks

		assert x_limits[0] <= bar_xticks[0].get_position()[0]
		assert x_limits[1] >= bar_xticks[-1].get_position()[0]

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