BUG df.plot.box handles matplotlib Axes with sharey=True (#54940)

* BUG manage sharey in plot.box with vert=False

* fix

* add entry in whats new

* iter

Author: glemaitre

Diff for: doc/source/whatsnew/v2.2.0.rst

@@ -288,7 +288,7 @@ Period
 
 Plotting
 ^^^^^^^^
--
+- Bug in :meth:`DataFrame.plot.box` with ``vert=False`` and a matplotlib ``Axes`` created with ``sharey=True`` (:issue:`54941`)
 -
 
 Groupby/resample/rolling

Diff for: pandas/plotting/_matplotlib/boxplot.py

@@ -40,6 +40,24 @@
     from pandas._typing import MatplotlibColor
 
 
+def _set_ticklabels(ax: Axes, labels: list[str], is_vertical: bool, **kwargs) -> None:
+    """Set the tick labels of a given axis.
+
+    Due to https://github.com/matplotlib/matplotlib/pull/17266, we need to handle the
+    case of repeated ticks (due to `FixedLocator`) and thus we duplicate the number of
+    labels.
+    """
+    ticks = ax.get_xticks() if is_vertical else ax.get_yticks()
+    if len(ticks) != len(labels):
+        i, remainder = divmod(len(ticks), len(labels))
+        assert remainder == 0, remainder
+        labels *= i
+    if is_vertical:
+        ax.set_xticklabels(labels, **kwargs)
+    else:
+        ax.set_yticklabels(labels, **kwargs)
+
+
 class BoxPlot(LinePlot):
     @property
     def _kind(self) -> Literal["box"]:
@@ -193,7 +211,9 @@ def _make_plot(self) -> None:
                 )
                 self.maybe_color_bp(bp)
                 self._return_obj[label] = ret
-                self._set_ticklabels(ax, ticklabels)
+                _set_ticklabels(
+                    ax=ax, labels=ticklabels, is_vertical=self.orientation == "vertical"
+                )
         else:
             y = self.data.values.T
             ax = self._get_ax(0)
@@ -209,13 +229,9 @@ def _make_plot(self) -> None:
             labels = [pprint_thing(left) for left in labels]
             if not self.use_index:
                 labels = [pprint_thing(key) for key in range(len(labels))]
-            self._set_ticklabels(ax, labels)
-
-    def _set_ticklabels(self, ax: Axes, labels: list[str]) -> None:
-        if self.orientation == "vertical":
-            ax.set_xticklabels(labels)
-        else:
-            ax.set_yticklabels(labels)
+            _set_ticklabels(
+                ax=ax, labels=labels, is_vertical=self.orientation == "vertical"
+            )
 
     def _make_legend(self) -> None:
         pass
@@ -382,16 +398,9 @@ def plot_group(keys, values, ax: Axes, **kwds):
             ax.tick_params(axis="both", labelsize=fontsize)
 
         # GH 45465: x/y are flipped when "vert" changes
-        is_vertical = kwds.get("vert", True)
-        ticks = ax.get_xticks() if is_vertical else ax.get_yticks()
-        if len(ticks) != len(keys):
-            i, remainder = divmod(len(ticks), len(keys))
-            assert remainder == 0, remainder
-            keys *= i
-        if is_vertical:
-            ax.set_xticklabels(keys, rotation=rot)
-        else:
-            ax.set_yticklabels(keys, rotation=rot)
+        _set_ticklabels(
+            ax=ax, labels=keys, is_vertical=kwds.get("vert", True), rotation=rot
+        )
         maybe_color_bp(bp, **kwds)
 
         # Return axes in multiplot case, maybe revisit later # 985

Diff for: pandas/tests/plotting/test_boxplot_method.py

@@ -329,6 +329,22 @@ def test_plot_xlabel_ylabel(self, vert):
         assert ax.get_xlabel() == xlabel
         assert ax.get_ylabel() == ylabel
 
+    @pytest.mark.parametrize("vert", [True, False])
+    def test_plot_box(self, vert):
+        # GH 54941
+        rng = np.random.default_rng(2)
+        df1 = DataFrame(rng.integers(0, 100, size=(100, 4)), columns=list("ABCD"))
+        df2 = DataFrame(rng.integers(0, 100, size=(100, 4)), columns=list("ABCD"))
+
+        xlabel, ylabel = "x", "y"
+        _, axs = plt.subplots(ncols=2, figsize=(10, 7), sharey=True)
+        df1.plot.box(ax=axs[0], vert=vert, xlabel=xlabel, ylabel=ylabel)
+        df2.plot.box(ax=axs[1], vert=vert, xlabel=xlabel, ylabel=ylabel)
+        for ax in axs:
+            assert ax.get_xlabel() == xlabel
+            assert ax.get_ylabel() == ylabel
+        mpl.pyplot.close()
+
     @pytest.mark.parametrize("vert", [True, False])
     def test_boxplot_xlabel_ylabel(self, vert):
         df = DataFrame(